Iron-based corrosion resistant wear resistant alloy and deposit welding material for obtaining the alloy

ABSTRACT

To provide a high-performance, inexpensive low C-high Si-high Cr—B—Nb type iron-based corrosion-resistant and wear-resistant alloy that is extremely superior in corrosion resistance and wear resistance to 304 stainless steel, high-chromium cast iron and high carbon-high chromium cast-iron-type materials, has a high corrosion-resistant property that would never be obtained from a high carbon-high chromium carbide precipitation-type iron-based wear-resistant alloy and at the same time, a wear-resistant property that is superior to these metals, and further hardly causes brittle peeling that is inherent to high Si—containing steel. This alloy contains, all percentages by weight, C: 0.5 to 2.5% by weight, Si: 2.5 to 4.5%, Mn: 0 to 10% or less, Cr: 15% to 31%, Ni: 0 to 16%, Cu: 7% or less, Mo: 10% or less, B: 0.5% to 3.5%, and 0≦Nb+V≦8%, and in this structure, within a range of 15% Cr≦Cr&lt;27%, (Si×B)≦2014/Cr 2 +0.083Cr+1.05 is satisfied, within a range of 27%≦Cr≦31%, 1.25%≦(Si×B) 6.0% is satisfied, within a range of 15%≦Cr&lt;20%, (Si×B) 570/Cr 2 −0.066Cr+1.145 is satisfied, and within a range of 20%≦Cr≦31%, (Si×B)≧1.25 is satisfied.

TECHNICAL FIELD

The present invention relates to a low carbon-highsilicon-boron-niobium-high chromium cast steel-type iron-based alloythat is superior in corrosion resistance and wear resistance, morespecifically, to a high performance and inexpensive iron-basedcorrosion-resistant and wear-resistant alloy that is overwhelminglysuperior in a corrosion-resistant property and wear-resistant propertyin comparison with those of 304 stainless steel, high-chromium castiron, and high carbon-high chromium cast-iron-type material, has a highcorrosion-resistant property that would never be obtained from a highcarbon-high chromium carbide precipitation-type iron-basedwear-resistant alloy and at the same time a wear-resistant property thatis superior to that of these metals, and further hardly generate brittlepeeling that is inherent to a high-Si content steel, and a clad(hard-surfacing) welding material used for obtaining the same.

BACKGROUND ART

In recent years, refuse incinerating factories, car-shredderfluidizing-layer incinerators, waste oil and waste fluid incineratorsand the like have been built and operated. In heat-resistant andwear-resistant portions of these devices, high chromium cast iron isused, and in the devices that are subjected to high—temperature thermaloxidization, for example, SCH13 heat resistant cast steel or the like isused. However, in a short period of time after the start of theseoperations, those members and devices are worn, burnt to be lost, andsubjected to corrosive loss by the treated matters and heat, and therehave been strong demands for prolonging the service life thereof.

With respect to the life-prolonging countermeasures for these devicesand members, repairing processes by clad welding are mainly carried outon worn-out portions, and a high carbon-high chromium cast iron-typeclad welding material that is an iron-based alloy has been mainly usedas its welding material. The reasons for this are because the iron-basedalloy is inexpensive and it is superior in a wear-resistant property andhigh-temperature oxidation resistant property. However, these furnacedevices and peripheral devices are exposed to such as high-temperaturecorrosive burning gases and acid dew-point corrosion that occurs uponstopping the furnace, and at present, it becomes difficult to deal withthese conditions only by using simple high-temperature oxidationresistant property and wear-resistant property.

That is, unless a superior corrosion-resistant property is alsoprovided, with a superior wear-resistant property possessed by the highcarbon-high chromium cast iron-type clad welding material beingmaintained, it becomes difficult to prolong the service life of thesevarious devices. In particular, with respect to the corrosionresistance, corrosion-resistant properties against chlorine gas,hydrochloric acid, sulfuric acid, diluted sulfuric acid and the like arerequired.

With respect to these application environments that call for acorrosion-resistant property, an oxidation resistant property and ahigh-temperature wear-resistant property, stellite that is acobalt-based alloy is particularly superior in comparison with theiron-based clad welding material, and the application thereof as thecladding material has been proposed. However, this alloy is veryexpensive in comparison with the iron-based alloy, failing to satisfythe cost-effectiveness balance. For this reason, there have been strongdemands for developments of an iron-based clad welding material that isinexpensive and has the same performances (Non-Patent Document 1).

Non-Patent Document 1: “Basics and Applications of Surface TreatmentTechniques” (Vol. 1) Textbook for 14^(th) Practical Welding Seminar,East Branch of Welding Society, Jun. 23 to 24, 1988

In addition to these, using expensive alloys having rarity-value metalelements, such as nickel, cobalt and the like, as simple disposablewear-resistant materials is very wasteful from the viewpoint of theinternational trend of resource-saving movements, and originally, theseexpensive alloys should be effectively utilized as permanent materialshaving high value and applications capable of recovering resources;thus, the present inventors have always thought that inexpensiveiron-based wear-resistant alloys should be used for disposableapplications such as wear-resistant materials.

Then, at present, since the high carbon-high chromium cast-iron-typeclad welding material is inexpensive, this has been continuously used inmost cases as the iron-based wear-resistant alloy; however, thecorrosion-resistant property thereof is extremely inferior to that ofcobalt- and nickel-based materials, and this is hardly called as acorrosion-resistant material. The typical composition of the highcarbon-high chromium cast-iron-type clad welding material that has beenmainly used conventionally is “C: 3 to 6%, Cr: 16 to 36%, Mo: 0 to 3%,Fe: remaining portion.”

However, alloys belonging to this type are extremely superior in wearresistance, and although these are iron-based alloys, they areconsiderably superior in high-temperature oxidation resistance becauseof the high chromium content, and have been often used forhigh-temperature wearing applications at 600° C. as well as at 600° C.or more. One of typical examples thereof is an alloy having thefollowing chemical components: “C: 5.2%, Cr: 32%, Si: 0.6%, Mn: 0.7%,Fe: remaining portion.”

This iron-based wear-resistant clad welding metal has a superiorwear-resistant property, that is, a wear test value of 5.0 to 10, ifindicated by a wear coefficient, with that of SS400 mild steel being setto 100, which is a wear-resistant property about 10 to 20 times higherthan that of the mild steel. However, since this has a carbon contentthat is extremely high, it can be said that the corrosion resistance isnot sufficient.

For this reason, the present inventors have tried to develop aninexpensive iron-based alloy that has a wear-resistant property that isthe same as, or equivalent to that of this high carbon-high chromiumcast-iron-type clad welding alloy, a corrosion-resistant property thatis close to that possessed by cobalt alloys, stellites No. 1 and No. 6,and exerts a corrosion-resistant property that is the same as, or higherthan that with respect to certain kinds of corrosive media. Here,colmonoy No. 6 alloy has been well known as a nickel-based alloy havinga superior wear-resistant property. The wear coefficient WR thereof is5, which is somewhat superior than WR=8 of stellite No. 1; however, withrespect to the sulfuric acid corrosion resistance, this is inferior tothat of the stellite alloy so that the target of the present inventorsis still placed on the cobalt-based stellite alloy, and if thecorrosion-resistant property of the iron-based alloy becomes higher thanthat of the cobalt-based alloy, the iron-based alloy has been determinedas being superior to that of the nickel-based alloy. The standardcompositions of stellite No. 1 and No. 6 are shown below:

[Standard chemical components of cobalt-based alloy: stellite No. 1]

“C: 2.1%, Si: 0.8%, Mn: 0.4%, Cr: 32.0%, Fe: 2.0%, W: 12.0, Ni: 1.7, Mo:0.1, Co: remaining portion”

[Standard chemical components of cobalt-based alloy: stellite No. 6]

“C: 1.2%, Si: 0.8%, Mn: 0.5%, Cr: 27%, Ni: 2.7%, W: 4.5%, Fe: 2.5%, Mo:0.1%, Co: remaining portion”

Upon reviewing alloy elements contained in these cobalt-based alloys, itis found that large amounts of cobalt, tungsten and the like arecontained so that these alloys are composed of very expensive elements.Therefore, since the cobalt-based alloys are very expensive alloys,these do not become profitable when applied to a device having a verywide cladding area from the viewpoint of costs, and it is very difficultto satisfy the cost-effectiveness.

For this reason, the use of this alloy is considered to be limited onlyto applications in which a cladding process on a portion having anextremely limited small area can exert a great effect. Theseapplications include various valve sheets, for example, a tip of aneedle valve, a pump rod, a pump sleeve, a cam shaft and the like.Stellite No. 1 and No. 6 alloys are used for applications calling forthree factors as heat resistant, corrosion-resistant and wear-resistantalloys simultaneously, and, in particular, suitably used forapplications having a temperature of 600° C. or more, and these arepopular alloys in the world. However, at present, these have also beencontinuously used for applications at 600° C. or less in many cases, soas to carry out a cladding process in devices in whichcorrosion-resistant and wear-resistant properties are required.

Using alloys containing expensive rare elements for even applications at600° C. or less as simple wear-resistant members is an anti-socialpractice from the viewpoints of wasteful use of resources in the worldand of exhaustion of resources in the future as described earlier, andexpensive rare elements should be used for significant applicationshaving high value, and should also be used for applications capable ofrecovering resources.

Consequently, the present inventors have proposed a highlywear-resistant “clad welding material and a clad member” that is aninexpensive iron-based alloy and exerts a superior high-temperatureoxidation resistant property at a high temperature of 600° C. or more,as one of means for solving these problems and achieving improvements asmuch as possible, and have granted a patent thereof (Patent Document 1).This patented alloy exerts performances superior to those of stelliteNo. 1, when cladded on a device calling for a high-temperaturewear-resistant property, an oxidation resistant property and acorrosion-resistant property in applications of 600° C. or more, andmakes it possible to cut costs to a great degree.

Patent Document 1: U.S. Pat. No. 3,343,576

Typical practical examples include: cladding processes for a scrapinglifter of a rotary kiln to be used at an ambient temperature of 800 to900° C., a falling inlet liner of a clinker cooler to be used from 900to 1000° C., a copper-resource recovering clinker grizzly bar used at900° C. or more, a clinker transporting conveyer bucket of 800° C., afluidizing bed furnace boiler tube, a wire of air blowing nozzle and thelike, and by many application achievements relaxing to these claddingprocesses, the patented alloy has devoted to a great reduction in costsby means of prolonged service life. A typical composition of componentsand performances of this patented cladding alloy are shown below:

[FREA-METAL chemical components (% by weight) of No. 55 alloy]

Fused metal composition “C: 1.3%, Si: 4.5%, Ni: 3.7%, Mn: 3.6%, Cr: 36%,Fe: remaining portion”Base material: SUS310S 9 mmt

Hardness: HV977

Wear coefficient: 4.2First layer Cr analyzed value: 35%Micro texture: ×400 (photograph No. 1 in FIG. 2)

Moreover, a test piece No. 55 that was subjected to a bending process(bending radius: 290 mmR) with its hardened metal being placed insidethereof is shown by photograph No. 2 in FIG. 2. Here, the alloy Nos. arethose adopted in composition comparison tests that will be describedlater (see FIG. 1).

The greatest feature of this patented alloy is that a high Si-contentwas given to a high chromium iron-based alloy exceeding 30%. Here, Si isvery inexpensive in comparison with expensive elements such as V, W, Mo,Co, Ni and the like that give a high-temperature resistant property anda heat resistant property, and when obtained from silica by using areducing process, it is possible to utilize materials that inexhaustiblyexist on the earth. However, the greatest defect of the highSi-containing steel is to make the alloy extremely brittle, and becauseof this defect, a large amount of addition thereof to an iron-basedwear-resistant cladding metal has been avoided even at present.Nevertheless, the present inventors have still been paying attention tocharacteristics of Si, that is, the fact that it is an inexpensiveelement that inexhaustibly exists on the earth, its high-temperatureoxidation resistant property and its property for allowing chromiumcarbides to be formed into a needle-shape, and such a high content asnot to be used or to be avoided normally, that is, 3.0 to 7.0%, wasadded thereto.

Incidentally, although a high Si-containing steel referred to as“Silicolloy” has already been produced, this metal was an alloydeveloped for use in wear-resistant purposes between metals, and itscarbon content was in a level of 1/100 so that the amount ofprecipitation of carbides that give a wear-resistant property wasextremely small, failing to be practically used in severelyhigh-temperature grinding wear-resistant applications, as in the case ofthe application of the patented alloy (Patent Document 2).

Patent Document 2: JP-A No. 54-81115

The deposited metal of a high Si-containing steel has a characteristicof causing slice-shaped surface layer peeling on the surface layer, withthe result that, upon carrying out a bending process thereon, there is afear of scattering of slice-shaped portions. When further pressed andbent strongly, the deposited metal is fractured to drop off the basematerial. By viewing the bending test piece No. 55 of the wear-resistantalloy, the typical peeling state can be confirmed. Consequently, thepatented alloy has been mainly used in the form of a welding rod and aclad welding wire that are hardly subjected to a bending process.

In this manner, the above-mentioned patented alloy has been developed byadding Si hoghly, and the alloy is used for high-temperaturewear-resistant applications of 600° C. or more, and makes it possible toprovide a high-temperature oxidation resistant property as high as thatof SUS310S in spite of the fact that it is an iron-based alloy, and toremarkably improve the high-temperature wear-resistant property andhigh-temperature hardness by allowing a large amount of needle-shapedchromium carbides that hardly drop off to be precipitated at hightemperatures. In particular, under a high-temperature condition from 600to 1000° C., the alloy becomes rich in ductility in comparison with anormal temperature state so that its brittleness is alleviated, andfurther a large amount of Si was solid-deposited on the matrix base inthe deposited metal so that it contributes to improvements of thehigh-temperature oxidation resistance of the matrix, making it possibleto endure even at a high temperature of 1000° C.

In particular, a condition “Cr%≧−1.6Si %+37Cr %”, which forms a base forconstituting the patented alloy, is a two-element correlation formulabetween Cr and Si that accelerates a large amount of needle-shapedchromium carbide precipitation required for ensuring a superiorwear-resistant property at 600° C. or more. Without satisfying thiscorrelation formula, a sufficient precipitation of needle-shapedchromium carbides (Cr₇C₃) is not available, resulting in degradation ofthe high-temperature wear resistance.

The natural characteristic of normal metal is such that, within ahigh-temperature range of 600° C. to 1000° C., the hardness of a metalmatrix softens extremely so that wear is easily accelerated; however,since needle-shaped carbides are conjugated in the width direction whilebeing entangled with one another over the entire matrix like knittingfibers, selective wear of soft matrix portions is prevented; thus, theabove-mentioned patent alloy technique is based upon the fact that byallowing a large amount of high-hardness needle-shaped carbides to becrystallized, high-temperature wear can be prevented. By viewing thetexture of this alloy, a precipitation of the remarkable needle-shapedcarbides can be confirmed (photograph No. 1 in FIG. 2).

However, the superior characteristic at high temperatures in contrastbecomes a serious defect in its brittleness at normal temperature, andthe extreme brittleness causes degradation of the bendingprocessability, and when a wear-resistant steel plate cladded with thepatented alloy is produced, the resulting product can be only applied tolinear items, and with respect to items having a curvature, claddingprocesses need to be carried out by using a welding wire or a handwelding rod, always resulting in high production costs.

As described above, although the patented alloy can provide performancesthat are almost equivalent to the stellite alloy, its greatest defect isthat the high Si-content easily causes slice-shaped peeling on thesurface layer of the deposited metal, making it difficult, inparticular, to produce a wear-resistant steel plate having a large area.Moreover, upon carrying out a join-welding process between clad steelsformed by using the same alloy, the hardened metal causes peeling whenstretched by a welding stress, making it very difficult to carry out thejoin-welding process.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to provide a low carbon-highchromium-high Si-boron-niobium-cast-iron-type iron-basedcorrosion-resistant and wear-resistant alloy that can alleviatebrittleness which is a defect of a high Si-containing steel, maintain anoverwhelming corrosion-resistant performance in comparison with that ofa high chromium cast-iron-type cladding alloy or 304 stainless steel,exerts performances that are the same as, or higher than those ofstellites No. 1 and No. 6 with respect to some corrosive environments,and has a wear-resistant property that is the same as, or higher thanthat of a high carbon-high chromium cast-iron-type cladding alloy orstellites No. 1 and No. 6, and a clad welding material used forobtaining the same.

Means for Solving the Problems

In order to achieve the above-mentioned object, in order to improve asulfuric acid resistant property that is a weak point of an iron-basedalloy, the present inventors have tried to find an alloy that is alsosuperior in a hydrochloric acid resistant property by appropriatelycombining a large amount of Cr and a small amount of Si, Mo, Cu, Ni andthe like and using as one model a Worthite alloy (C<0.07%, Cr20%, Ni25%,Si3.5%, Mo3% and Cu2%) that has been already developed, so as to developan inexpensive iron-based alloy having a corrosion-resistant propertyand a wear-resistant property that are the same as, or superior to thoseof stellites No. 1 and No. 6 that are expensive cobalt-based alloys.

The Worthite alloy is a Cr—Ni—Si—Mo—Cu type stainless steel developed byWorthington Pum Co., Ltd. in the United States, and this is used forsulfuric acid corrosion-resistant applications in chemical plants andboilers exclusively used for burning petroleum. Although the Worthitealloy is used as one model from the viewpoint of sulfuric acid corrosionprevention, the problem with this alloy is that it contains much Ni,which is different from the intention of the present inventors, and thatthis alloy differs greatly from the attempt to save resources such asrarity-value alloys, which is the original major premise. The Worthitealloy is mainly used as a corrosion-resistant structural material thatrequires strength, and utilized as, for example, pumps or the like madeof stainless cast steel. Therefore, it is important that the metalitself has toughness; however, the alloy becomes brittle because of itshigh Si-content, and it is assumed that the alloy is designed to have ahigh Ni-content so as to alleviate the brittleness. Of course, the highNi-content mainly aims to improve the corrosion-resistant property;however, this causes low hardness, and makes it inferior in thewear-resistant property as a wear-resistant hardened metal material, andthe resulting iron-based alloy is not applicable to a wear-resistantalloy in which the present inventors aim to produce.

Since a cladding alloy to be developed by the present inventorsbasically aims to simultaneously satisfy both of the corrosion-resistantproperty and the wear-resistant property, stainless steel is used as itsbase metal in many cases. For this reason, since the Ni content isexpected to increase by allowing the deposited metal to pick up Ni fromthe stainless steel or the like of the base metal, the present inventorsset the Ni content originally added to a welding material to 13% in themaximum level so as to save resources. That is, with respect to the Nicontent of the developed alloy, it is normally set to 5% or less, andthe addition thereof is set to 13% in the maximum level only in alimited occasion. On the other hand, concerning Si, the followingarrangement is made.

(1) Brittleness of High Si-Containing Steel

A high silicon steel plate is one of high Si-containing steels ofiron-based metal. One example of components thereof is shown below:

[C: 0.12%, Si: 4.12%, Mn: 0.07%, S: 0.005%, Fe: remaining portion]

The silicon steel plate is mainly used for transformers and motor cores.When the Si content is increased, its magnetic property is desirablymade greater; however, the addition of Si of 5% or more causes the steelto become brittle, and further addition of Si makes it difficult tocarry out a rolling operation, and causes a difficulty in producing athin steel plate. Here, Si has such a characteristic that, when onlyadded to simple carbon steel, the resulting steel becomes brittle. Inthe case where the same amount of Si is added to a high chromium alloycontaining much Cr, the tendency of brittleness possessed by Si itselfand highly hard and brittle chromium carbides precipitated by the highchromium alloy synergistically accelerate the brittleness of the alloy;therefore, it becomes very difficult to provide ductility to a developedalloy.

(2) Brittleness of High Si-Containing Steel and Effects of C Exerted onCorrosion Resistance and Wear Resistance

In order to improve the ductility of deposited metal, that is, toprevent the occurrence of peeling, and to improve the corrosionresistance, first, the carbon content is proposed as one of importantcomponent elements. A high carbon-high chromium cast-iron-type cladwelding material has a very high carbon content, and is included withina cast iron range containing carbon of 4.5 to 6.0%. As a result, a largeamount of brittle chromium carbides are precipitated to cause areduction in Cr content included in the matrix, resulting in extremedegradation of the corrosion resistance. That is, the greatest reasonfor degradation of the corrosion resistance of various high carbon-highchromium cast-iron-type clad welding materials is in that, in order toobtain a wear-resistant property, a large amount of carbon is containedtherein, and carbon is thus bonded with a carbide-forming element havinga strong affinity to carbon, that is, chromium, tungsten, vanadium,titanium, niobium, or the like, so that, by allowing a large amount ofhigh-hardness carbides to be precipitated in the metal matrix, thewear-resistant property is ensured.

It is said that the chromium carbide has a high hardness in a range ofHV1650 to 2100, the niobium carbide has that of HV2400, the titaniumcarbide has that of HV2800, the vanadium carbide has that of HV2800 andthe tungsten carbide has that in a range of HV2400 to 3000. Highchromium cast-iron-type alloys maintain a superior wear-resistantproperty by these carbides that are precipitated; however, in contrast,the corrosion-resistant property of the deposited metal deterioratesextremely because of the high carbon content.

In general, from an iron-carbon two-element state diagram, it is saidthat, with the carbon content of 2.0 to 2.1% being set as a border,those below the border are cast steels, while those above the border arecast irons. Moreover, since it is determined that the cast steel havinga carbon content of 2.0% or less is superior to the cast iron having acarbon content exceeding 2.0% in its mechanical properties, inparticular, in its toughness in the metal matrix, the developed weldingalloy has been designed so that the carbon content of the first-layerdeposited metal is set to 2% or less. It was assumed that the low carboncontent of course contributes to improvements of corrosion resistance.

In the case where the carbon content of a welding material is set to3.0% or less, upon determining from the amount of precipitation ofcarbides, a so-called hypo-eutectoid state is exerted, and when onelayer is cladded on a mild steel, a sufficient carbide precipitationdoes not occur on the first deposited metal due to melting-in of themild steel, resulting in serious degradation of the wear-resistantproperty. For example, even in the case where a carbon content of 3.0%is given to the welding material, upon cladding one layer on a mildsteel or stainless steel base material, the carbon content in thedeposited metal varies within a range of 1.8% to 2.1% although itdepends on the melt-in depth into the base metal (melt-in depth: about30% to 40%). This content corresponds to near 2.0% of carbon contentthat divides the cast steel and the cast iron from each other. Normally,the carbon amount to be contained in a high carbon-high chromiumcast-iron-type welding material needs to be set to 4.5% or more so thatit is important to maintain a hyper-eutectoid state in which asufficient carbide can be precipitated even under influences of dilutionof mild steel from the first layer. That is, even upon receipt of 30% ofmelting-in, the carbon content of the first layer deposited metal needsto be set to about 3% or more so as to form a hyper-eutectoid state.

Based upon above description, the upper limit value of the carboncontent of the first layer deposited metal of the developed alloy wasset to 2.0% or less that divides the cast steel and the cast iron fromeach other as one target value. For another reason, since the carboncontent of stellite No. 1 alloy of the cobalt-based alloy is C: 2.0%,and the criteria of the corrosion-resistant performance of the developedwelding material is determined as the same as, or not less than thecorrosion resistance performance of stellite No. 1, the carbon contentwas determined to virtually the same amount.

Table 1 shows comparisons of wear-resistant property depending ondifferences in carbon contents. Here, alloys No. 41 and No. 42 are highSi-containing steels, and since these contain neither Nb nor B, theseare not included within the developed alloy component range; however,since these are desirably used for comparing the wear-resistant propertydepending on differences in carbon amounts, they were listed.

TABLE 1 Effects of carbon content exerted on wear-resistant property (%by weight) Wear Alloy C Si Ni Cr Mo Cu Hardness coefficient 41 2.0 5.03.3 23 4.6 4.6 HV616 6.3 42 3.0 5.1 3.3 23 4.6 4.6 HV679 2.5

Alloy No. 41 and alloy No. 42 were produced by adjusting them to havevirtually the same chemical components except for the carbon contents.Alloy No. 42, which had a higher carbon content, provided awear-resistant property that is about 2.5 time higher than that of alloyNo. 41. This is because, since alloy No. 42 has a higher carbon content,the amount of precipitation of chromium carbides increases so that thewear resistance is improved.

The carbon content is one of factors that cause great adverse effects tothe corrosion-resistant property; however, in the case where the carboncontent is reduced so as to improve the corrosion-resistant property,the amount of precipitation of carbides is reduced to cause seriousdegradation of the wear-resistant property. Therefore, the presentinventors have revised component constitutions of a high carbon-highchromium cast iron that allows a large amount of carbides to beprecipitated by its high carbon content, and can ensure thewear-resistant property. That is, the target was to develop an alloywhich, even when it has an amount of carbon addition in a range of0.5%≦C≦2.0 to 2.5%, can ensure a superior wear-resistant property aswell as a superior corrosion-resistant property and sufficienttoughness. There are various different cladding methods with respect tothe clad welding materials, and the respective methods have differentmelting-in depths and subsequently different dilution rates in the basematerial, the maximum amount of addition of C was set to 2.5% or less.

(3) Effects of Cr Exerted on Brittleness and Wear-Resistant Property ofHigh Si-Containing Steel

Here, Cr is one of alloy elements that give greatest influences tobrittleness of a high Si-containing steel. The chromium content of thefirst layer deposited metal that has been actually cladded by using awelding material having a content of chromium addition of 45% in themaximum, becomes about 23 to 34% upon receipt of a base materialdilution in a range of about 25% to 50%, in the case where the basematerial is a mild steel or an esten steel. In the case of the amount ofchromium addition of 25%, the chromium content becomes about 15 to 19%.In the case where SUS304 to 316 is used as a base material, on theassumption of the use of a welding material of Cr: 35%, the chromiumcontent in the first layer deposited metal becomes about 26 to 31%.Although the melting-in depth differs depending on the welding methods,the Cr content of the first layer deposited metal is selected to be setto about “15%≦Cr≦31%” on average.

The maximum amount of addition of 45% is used for providing a handwelding rod having a base material dilution rate of 50% or more, andwhen the base material is mild steel, the chromium content of the firstlayer deposited metal becomes about 23%, and is included in theabove-mentioned range. In particular, in the case of a wear-resistantsteel plate, this is formed by using one-layer cladding process, and thethickness of the deposited metal becomes about 4 to 6 mm. With respectto the brittleness of the deposited metal obtained by a clad weldingmaterial and a wear-resistant steel plate, the behavior of the firstlayer deposited metal is considered to be most important. Therefore, itis necessary to properly design the range of the chromium content in thefirst layer deposited metal. The reason for this is because chromium isan element to be contained in a large amount in the developed alloy incomparison with the other alloy elements, and furthermore since this hasgreat influences to the brittleness of the deposited metal, theunderstanding of the degree of influences of each of the othersmall-amount added alloys is most essentially determined by the behaviorof this element within a predetermined range.

Incidentally, for the necessity of depositing a large amount ofneedle-shaped chromium carbides so as to provide a superiorhigh-temperature wear-resistant property at temperatures higher than600° C., it was very important that the above-mentioned patented alloysatisfies a two-element correlation formula between Cr and Si,“Cr≧−1.6Si+37 (% by weight)”. In the case where the Cr content is 32% ormore, with the Si content being 3% or more, a large amount ofneedle-shaped chromium carbides are precipitated to cause extremebrittleness and the subsequent peeling on the surface of the hardenedmetal; this phenomenon has been proved by No. 55 bending test piece (seephotograph No. 2 in FIG. 2).

On the contrary to the patented alloy, the developed alloy is not analloy formed by aiming in particular a high-temperature wear-resistantproperty, but an alloy formed mainly by aiming to ensure properductility of a brittle in high Si-containing steel as well as to improvethe corrosion-resistant property thereof by using an iron-based alloy.Therefore, since it is not necessary to satisfy the condition of“Cr≧−1.6Si+37Cr %”, the amounts of addition of silicon and chromium thatcause brittleness of the deposited metal can be reduced in comparisonwith those of the former; however, the reduction in the amounts ofaddition of Cr and Si causes a reduction in the amount of precipitatedchromium carbides, with the result that the wear-resistant property islowered extremely although the ductility is recovered.

This phenomenon has been proved by experiments to be discussed below. Inthe case where, by using the above-mentioned patented alloy as its basicalloy, the amount of Cr addition that gives greatest influences to thewear-resistant property was reduced from 36% to about 20 to 25%, thetoughness and wear-resistant property of the resulting alloy wereexamined. The examination of the toughness was carried out as follows: Awear-resistant steel plate on which a layer of a test alloy with athickness of 5 mm was deposited on a SUS310S base material having a sizeof 9 mm in thickness×100 mm in width×400 mm in length was formed, andthe toughness thereof was determined by using bending tests of 200R and290R. When even one portion of the deposited metal was peeled or chippedin this bending test, this state was determined as “poor in toughness”.Based upon the wear-resistant coefficient WR=15 or less possessed bystellite No. 6 as the standard, the wear coefficient WR was required toexceed this level. Table 2 shows the alloy compositions and Table 3shows the results of the examination.

TABLE 2 FREA-METAL Modified Alloy (added % by weight) Alloy C Si Mn NiCr Nb B 56 1.3 4.5 3.5 3.7 20 — — 57 1.3 4.5 3.6 3.7 20 0.6 1.0 58 1.34.5 3.6 3.7 20 0.6 2.0 69 1.3 4.5 3.6 3.7 20 8.0 — 70 1.3 4.5 3.6 3.7 258.0 —

TABLE 3 Test Results Applied base Wear Alloy material 200R 290R Hardnesscoefficient 56 310S ◯ ◯ HV309 78 57 310S ◯ ◯ HV351 37 58 310S ◯ ◯ HV42714 69 310S ◯ ◯ HV335 17 70 310S ◯ ◯ HV362 15

In spite of a high added amount of Si, all the alloys were acceptable(◯) in the bending performance, and the reason for this is presumablybecause, since the Cr content was small, the amount of precipitation ofneedle-shaped chromium carbides was small so that bending ductility wasimproved; in contrast, since the precipitation of carbides was small,the wear-resistant property was greatly lowered.

This test indicated that Cr, that is, chromium carbides, gives greatestinfluences to the toughness (bending ductility) and wear-resistantproperty. With respect to the wear-resistant property, two kinds ofalloys No. 58 and No. 70 became narrowly acceptable. In the case of a Cradded amount of 20% (content: about 21%) of No. 58 alloy as well as inthe case of a Cr added amount of 25% (content: about 25%), even uponaddition of the greatest amount of Nb of 8%, the wear resistance WRexhibited the lowest value of 14 to 15 so that it was found that it wasimpossible to adjust the wear-resistant property by adding Nb alone.

(4) Effects of Addition of B Exerted on Wear-Resistant Property andDuctility of High Si-Containing Steel

In the case of FREA-METAL alloy (No. 55) in which, since Cr and Sicontents were great, a large amount of brittle needle-shaped chromiumcarbides were precipitated in the matrix, peeling easily occurred in thebending process (see photograph No. 2 in FIG. 2). It is not possible torevise the characteristic that Si itself causes brittleness of steels.However, with respect to the developed alloy, although it has been foundthat the amount of precipitated chromium carbides greatly causesbrittleness of the resulting alloy, the chromium carbides also tend toform a needle shape as the Si content successively increases, and theshape of the chromium carbides also accelerates the brittleness, and isconsidered to form one of main causes that exert cracks and peeling tolower the wear-resistant property.

In order to improve the bending ductility, it is important to reduce alarge amount of crystallization of brittle needle-shaped chromiumcarbides. The wear-resistant property is lowered correspondingly as theamount of the needle-shaped carbides is reduced; therefore, bycrystallizing finely miniaturized compounds having high hardness, thatis, dispersed and crystallized spherical, island-shaped, network-shapedand indefinite shaped compounds, so as to compensate for the lowering,the deposited metal is prevented from becoming brittle, and this methodis considered to be the best means.

To provide a means for improving the wear-resistant property withoutcausing brittleness in high Si-containing steels, an attempt was made toimprove the wear-resistant property by crystallizing a boride havingextremely high hardness that gives no adverse effects to thecorrosion-resistant property, or by allowing a niobium carbide that hasa strong affinity with carbon and crystallizes spherical miniaturizedcarbides so as to coexist therewith. At the same time, it was expectedthat these two elements would not give adverse effects to causebrittleness, and the subsequent peeling and drops-off of the surfacelayer metal, which is the greatest defect of the high Si-containingsteel, and would rather serve to suppress the brittleness.

In a chromium content in the deposited metal within a range from15%≦Cr≦31%, the wear-resistant property can be improved by adding boronthereto; however, in the addition of boron alone, for example, theaddition of 0.5% did not improve the wear-resistant property, while theaddition of 4.0% caused the deposited metal to become extremely hard,resulting in many cracks developing in a right-angle direction relativeto the welding bead. The addition of B alone caused a narrowed range ofthe amount of addition, making it very difficult to determine the degreeof ductility of the deposited metal. Upon comparison in wear-resistantproperty between the low-B content steel and the high-B content steel,although the high-B content steel exerted a superior wear-resistantproperty, it also caused serious brittleness. The effects of addedamount of boron exerted on the wear-resistant property and bendingprocessability are shown in Table 4.

TABLE 4 Effects of added amount of boron exerted on wear-resistantproperty and bending processability C Si Ni Cr Mo Nb B Cu Hardness WRLow-B 1.5 3.5 3.3 23 4.6 4.0 0.5 4.6 602 9.2 High-B 0.5 3.6 3.3 24 4.6 04.0 4.5 744 2.0 Cr: content (first layer fused metal)

Moreover, the high silicon content, which is the largest characteristicof the developed alloy, serves as a very effective factor tohigh-temperature oxidation resistance, sulfuric acid corrosionresistance, hydrochloric acid corrosion resistance and organic acidcorrosion resistance; however, normally, the addition of 3.5% or more toa normal iron-based alloy tends to cause serious brittleness to thealloy, with the result that this has not been used so much as aniron-based clad welding material, in spite of its superior performance.When the added amount of Si in a high Cr-content steel is increased, thechromium carbides are easily formed into a needle shape, with the resultthat the deposited metal tends to become brittle, and upon the additionof 5% of silicon alone, surface layer peeling occurred on the depositedmetal, while the reduction thereof to 2.5% causes serious degradation ofthe wear-resistant property. Therefore, the amount of Si addition thatfeatures the developed alloy is essentially set in a range from 2.5% inthe minimum to 4.5% to 5.5% in the maximum, and it was the absolutecondition to eliminate brittleness within this range of the addedamount.

In the same manner as in B, the addition of Si alone also caused anarrowed range of the amount of addition, making it very difficult toevaluate the ductility and wear-resistant property of the depositedmetal. Therefore, the use of the product Si×B (% by weight) was requiredas a method for evaluating B and Si with the influences of both of thembeing included. Here, B crystallizes borides to cause extremely highhardness, and it is considered that the kinds, shapes and sizes of theborides and the amount of crystallized borides give influences to theductility of the steel. In particular, in the case where the size wasextremely small in comparison with the size of needle-shaped chromiumcarbides, it was assumed that factors that accelerate physical damagesduring the bending process would be greatly reduced. It was alsoexpected that when the hardness of minute borides was extremely high,the wear-resistant property of the deposited metal would be improved.

Therefore, No. 10-C alloy that exerted superior results in sulfuric acidresistance and hydrochloric acid resistance was taken up, and carbidesand borides to be crystallized in the alloy were identified by using aSEM-EDX analyzer. Crystallized matters included a Cr₇C₃ chromium carbide(about HV2100) and three kinds of borides Cr₂B (about HV1400), Mo₂FeB₂(about HV2400) and NbB (about HV2250). All of these accounted for 30% ofthe total deposited metal. With respect to the shapes of thesecrystallized matters, Cr₇C₃ had a petal shape or a branch shape, andamong borides, NbB had an indefinite shape, Cr₂B had a plate shape, andMo₂FeB₂ had a net-work shape (see photograph 1 in FIG. 3).

Since the carbon content of No. 10-C alloy was about 0.7% to 0.8% thatwas a low level, only the boride Cr₇C₃ was crystallized with respect tocarbides, and with respect to Nb, no niobium carbides were produced.However, niobium borides (NbB) were crystallized to cause high hardnessequivalent to that of the niobium carbides. Therefore, it was clarifiedthat in the case where the carbon content was small, Nb forms borides tocontribute to improve the wear-resistant property. It was clarified thatbecause of these crystallized borides, the superior wear-resistantproperty was exerted even under a low carbon content.

Since, as the carbon content increases, more niobium carbides aresimultaneously crystallized so that they further contribute to improvethe wear-resistant property. By adding B and Nb so as to coexist, thewear-resistant property was successfully improved by their superiorhardness, without causing degradation of the bending ductility. Amongvarious kinds of boride crystallized matters, those that are assumed tocause brittleness of the alloy by their shapes include chromium boride(Cr₂B). Although these have a plate-shaped texture, the shapes thereofare similar to those of minute needle-shaped chromium carbides so thatthe brittleness might be caused (see photograph 1 in FIG. 3). In anactual bending test, No. 10-C alloy was easily bent and processed, withno surface layer peeling caused by the bending process (see photograph 2in FIG. 3). Probably because of a difference of the amount of producedcrystals from that of the needle-shaped chromium carbides, there was notso much influence given to the bending processability. With respect tothe hardness of borides, reference was made to “Handbook of MetalChemistry Thermal Processes (written by G. V. Boricenork).”

(5) Correlation between Si×B and Cr content

The correlation between the product of added amounts Si×B and Cr contentcan be considered as a correlation with the amount of crystallizedneedle-shaped chromium carbides that most greatly develop brittleness.When the Cr content is small, the amount of crystallized Cr carbides isof course reduced so that the tendency of brittleness is also reduced;however, in contrast, the wear-resistant property is greatly lowered. Inthe case where the amount of addition of Si alone is greatly increased,the tendency of causing brittleness to the metal becomes stronger due tothe tendency of causing brittleness and the characteristic of formingchromium carbides into a needle shape inherently possessed by Si;therefore, examinations were carried out so as to find out what degreethe ductility and the wear-resistant property were improved to by addingB so as to coexist, and how the appropriate alloy composition rangecould be subsequently expanded.

In the case of a low Cr-content, the product Si×B was set to 7.5 or morein a high level, and in the case of a high Cr-content, the product Si×Bwas set to 1.55 to 6.4 in a low level, so that the alloy compositionrange that would simultaneously satisfy the ductility and wear-resistantproperty of the alloy was examined. Tables 5 and 6 show the results ofthe examinations.

TABLE 5 Si × B Alloy (% by weight) Alloy C Si Mn Ni Cr Nb B 73 1.5 4.0Cu4.6 20 3.0 74 1.5 3.5 Cu4.6 20 3.0 75 1.5 2.5 Cu4.6 28 3.0 76 1.5 3.1Cu4.6 30 0.5 77 1.5 4.5 Cu4.6 30 0.5 78 1.5 3.2 Cu4.6 30 2.0 79 1.5 4.5Cu4.6 30 1.0 80 1.5 3.5 Cu4.6 30 1.0

TABLE 6 Test Results Applied Wear Acceptance base Cr Si × Hard- coef- orAlloy material 200R content B ness ficient unsuitability 73 SS400  15%12.0 HV686 5.0 Unsuitable 74 SS400  15% 10.5 HV726 6.3 Unsuitable 75304 ◯ 26% 7.5 HV654 6.1 Acceptable 76 304 ◯ 27% 1.55 HV450 67.0Unsuitable 77 304 ◯ 27% 2.25 HV460 17.0 Unsuitable 78 304 ◯ 27% 6.4HV603 12.4 Acceptable 79 304 ◯ 27% 4.5 HV455 30.7 Unsuitable 80 304 ◯27% 3.5 HV457 19.4 Unsuitable

In the case of the upper limit value of 7.5 of Si×B, although thewear-resistant property was ensured; however, the further additionthereof failed to ensure the bending ductility, while in the case of thelower limit value of 6.4 of Si×B, although the bending ductility wasensured, the further reduction thereof caused the wear-resistantproperty to be unsuitable, with the result that upper and lower width ofthe adjusting range became very narrow, with the upper limit value beingset to 6.1 and the lower limit value being set to 12.4 with respect tothe wear coefficient, failing to provide a superior wear-resistantproperty. The alloy composition range that would simultaneously satisfyboth of superior ductility and wear-resistant property was obtainedwithin only a limited range having a narrow width. Thus, it wasdifficult to obtain an alloy composition range having a wide width thatwould simultaneously satisfy the ductility and the wear-resistantproperty based upon only the correlation between the product of Si×B andCr.

(6) Effects of Added Nb

It is found that in particular, the lower limit value of Si×B providesan excellent bending ductility, but in contrast causes seriousdegradation of the wear-resistant property. The addition of each of Band Nb alone is not so effective; however, it is assumed that by addingthese so as to coexist, the wear-resistant property at the lower limitvalue would be greatly improved. With this arrangement, it is consideredthat the alloy composition range that satisfies both of the ductilityand the wear-resistant property can be greatly expanded.

Although Si×B of No. 35 alloy was 1.8, it became possible to ensure awear coefficient WR=9.3 by adding Nb=4.0% and AL=2.0%. In the case ofSi×B=3.5 of No. 33 alloy, a wear coefficient WR=5.9 was obtained byadding Nb=4.0%. Since the lowest reference value of the wear coefficientWR indicating the wear-resistant property is 15, this range issufficiently located within the reference values so that it becomespossible to greatly expand the alloy composition range thatsimultaneously satisfies the ductility and wear-resistant property byadding Nb and B so as to coexist.

In the product of Si×B, Nb is considered to be the third effectiveelement to improve the wear-resistant property, and this can be selectedwithin a very wide width of the added amount thereof, that is, a rangefrom 0 to 8.0% including no addition, so that it is expected to easilyadjust the wear-resistant property by using this. It is a known factthat Nb is an element that form carbides into a finely spherical shape,and since this has less possibility to cause brittleness of the metaland niobium carbides (about HV2400) and niobium borides (about HV2250)give high hardness, the wear-resistant property can be improved.

In the case where a gray pig iron has a needle-shaped graphite in itsgraphite shape, since the graphite causes brittleness in the resultingcast product, a method is proposed in which by adding Mg and Ca thereto,the graphite is formed into a spherical shape so that the ductilityequivalent to that of mild steel is prepared; however, the addition ofNb exerts the same effects as those of Mg and Ca with respect tocarbides. In the case where the carbon content of an alloy is set to avery low level, such as, to 0.5%, produced crystals of carbides aregreatly reduced; however, by adding boron thereto so that niobium boride(NbB) and chromium boride (Cr₂B) are dispersed and crystallized, thewear-resistant property is subsequently improved.

In this manner, both of B and Nb form fine crystallized matters toprevent brittleness of the present developed alloy, and by exchangingbrittle needle-shaped chromium carbides with both of these, it becomespossible to recover the ductility of the steel, and consequently togreatly improve the wear-resistant property by their high hardness. Ashas been already proved by the experiments, although the effect of theaddition of Nb alone failed to provide a sufficient wear-resistantproperty, it was possible to improve the wear-resistant property byallowing B to be added so as to coexist therewith.

The essential conditions of the developed alloy include the product ofSi×B and the addition of Nb to coexist, and lacking either one of thesemakes it very difficult to ensure a wide range of alloy compositionsthat sufficiently satisfy both of the ductility and wear-resistantproperty.

It is greatly beneficial that the brittleness in the high Si-containingsteel, which was the biggest conventional defect of the highSi-containing steel, can be alleviated by appropriately combining threeelements of Si, B and Nb, and it becomes possible to effectively utilizeSi that is inexpensive and gives a superior wear-resistant property anda high-temperature oxidation resistant property to a wear-resistantmaterial for iron-based alloys, in the future. With this arrangement, itis proposed to effectively utilize Si in place of an expensive alloyelement having a rarity value, such as Co, Ni and the like, and since itis possible to provide superior corrosion-resistant property againsthydrochloric acid and chlorine gas corrosions, the utilization thereofwas effectively expanded so as to be applied to hydrochloric acidcorrosion resistant and sulfuric acid corrosion resistant purposes inindustrial wastes, high-temperature burning furnaces, thermaldecomposing devices and fluidizing bed furnaces.

Assuming that a bending test is most simple and accurate as a method forevaluating brittleness of an alloy, a bending process was carried out toevaluate its ductility. The bending processability and thewear-resistant property were collectively summarized based upon thecorrelation between the chromium content and the product of Si×B. As aresult, with respect to the tendency of the limit that causes neitherpeeling nor fractures in a deposited metal, even bending tests have beencarried out under a fixed curvature, in the case of a low Cr content,the product of Si×B becomes a high value, while in the case of a high Crcontent, the product of Si×B becomes a low value. The method forevaluating the bending processability based upon the product of Si×Bmakes it possible to greatly expand the evaluation range in comparisonwith an evaluation method by the use of B or Si alone, and consequentlyto determine performances more accurately.

(7) Ductility Evaluation and Wear Resistance Evaluation by BendingProcess of Wear-Resistant Steel Plate

Supposing that the highest Si content of 4.5% is set, a large amount ofneedle-shaped carbides are crystallized with the chromium content ofabout 30% or more, from the expression of Cr %≧−1.6Si %+37, and since Crbecomes about 31% when Si=4%, the range of the chromium content in thefirst layer deposited metal is set to “15%≦Cr−31%”. Moreover,appropriate component ranges of the main influential elements to be usedfor obtaining deposited metal that has a superior bendingprocessability, that is, superior ductility, were specified as follows:

15%≦Cr≦31% (content in first layer deposited metal)

0.5%≦C≦2.0% (added amount)

2.5%≦Si≦4.5% (added amount)

0≦Nb+V≦8.0% (added amount)

0.5%≦B≦3.5% (added amount)

Within these component specific ranges, an appropriate range of Si×Bgiving influences to the bending processability was found. The productof Si and B that would give superior bending processability withoutcausing brittleness to the matrix was in a range of “1.25≦Si×B≦11.5.”The schematic tendency showed that in the case of a Low Cr content, thenumeric value of Si×B became higher, while in the case of a highCr-content, the numeric value of Si×B became lower. In particular, asthe numeric value of Si×B became lower, the wear-resistant propertytended to be lowered, and Nb was added so as to compensate for thereduced wear-resistant property.

As the numeric value of Si×B became higher and higher, the depositedmetal tended to become more and more brittle, with the result that thebending processability deteriorated; therefore, in order to improve thebending processability, the numeric value of Si×B had to be set to a lowlevel. As the numeric value of Si×B became lower, the ductility of thedeposited metal was improved so that the bending processability wassubsequently improved; however, in contrast, since the wear-resistantproperty was lowered, Nb was added within a range of 0≦Nb+V≦8.0% so asto adjust the wear-resistant property. In the case where the numericvalue was high, that is, for example, in the range of 4.0≦Si×B≦11.5%,the amount of Nb addition was set within a range of 0.5 to 4%, that is,a low level; in contrast, in the case where the numeric value was low,for example, in the range of 4.0≧Si×B≧1.25%, the amount of Nb additionwas set within a range of 4 to 8%, that is, a high level so that thewear-resistant property was improved.

The developed alloy aims at the improvement of the corrosion-resistantproperty, and in the case where the chromium content in the first layerdeposited metal is set to 15 to 18%, that is, to a low level, carbon andchromium are combined with each other by welding heat to form a Cr₂₃C₆carbide along the crystal grain interface, and this carbide isprecipitated along the grain interface to cause a lack of Cr that isrequired for the corrosion—resistant property, resulting in apossibility of grain interface corrosion. By adding 0.5% or more of Nbthereto, Nb that has a stronger affinity to carbon than Cr is allowed tobind with carbon to exert an effect for suppressing the precipitation ofCr₂₃C₆.

The addition of Ti≦1.0% or less also aims at the same effect as that ofNb, and since Ti exerts an extremely strong affinity with oxygen sothat, determining that more losses would be generated during ahigh-temperature oxidizing reaction in the metal than those generated byNb, the amount of addition was set to 1%.

A method for evaluating the bending processability of deposited metal isdescribed as follows: A clad steel plate that was cladded with depositedmetal with a thickness of 5 to 6 mm as a single cladded layer over theentire surface of each of steel plates having a size of 9 mm in massthickness×100 mm in width×400 mm in length of SS400, SUS304 and SUS310Swas produced, and this was subjected to a bending process by a presswith the hardened metal placed on the inner side. A stellite No. 1alloy, which was a target material, was cladded on SS400 with two layershaving a thickness of 5 mm, by a gas welding process. The length of eachsample piece was set to about 200 mm.

The bending curvature was set to about 200R, and the bending ductilitywas evaluated in the following three-degree criteria: in the case whereno influences were caused on the hardened metal by the bending and anappropriate bending performance was obtained without causing anydefects, this state was evaluated as ◯, in the case where severalsurface-layer peeling and extremely slight cracks occurred on thesurface of the hardened metal, this state was evaluated as ▴, and in thecase where many surface-layer peeling and lamp-shaped cracks occurred tocause poor toughness, this state was evaluated as . The results areshown in Table

In FIG. 1, Si×B is plotted on the axis of ordinates and the Cr contentof the first layer deposited metal is plotted on the axis of abscissasso that the relationship between these and the ductility was indicated.A curve on the upper portion indicates a fracture limit line ofsurface-layer face peeling and drops-off occurred on the deposited metalduring the bending process of the clad steel plate with a curvature of200R, and the upper side from this line indicates that the bendingprocess easily causes fractures. The lower curve indicates a limit linewhere the low-stress wear coefficient WR possessed by the depositedmetal is maintained at 15, and the lower portion below this indicates agreat reduction in the wear-resistant property with an increase in thewear coefficient.

Within an appropriate component range surrounded by the upper and lowerlimit lines, the bending processability of the wear-resistant steelplate composed of one cladded layer can be subjected to an R-bendingprocess up to a radius of 200 mm with respect to the curvature, andthere are many alloys capable of being subjected to a bending processwith a minimum curvature lower than this. The bending processability isthe same as, or superior to that of stellite No. 1, and a bendingprocess performance that is the same as, or superior to that of a highcarbon-high chromium cast iron alloy used for a wear-resistant steelplate is obtained. Alloys that can be subjected to such a minimum Rbending process among high S-content steels have not been known from thepast to the present.

The next important characteristic is an improved wear-resistant propertyat normal temperature. As has been described earlier, since the carboncontent that is the most essential factor for improving thewear-resistant property is greatly reduced in comparison with that of ahigh-chromium cast-iron-type cladded alloy, the wear-resistant propertyis lowered although the bending process performance and thecorrosion-resistant property are improved so that it becomes importantto ensure a sufficient wear-resistant property.

A method for determining and evaluating the wear-resistant property wascarried out by using an endless-belt grinder abrasion tester. The wearcoefficient of each of various alloys was calculated by a ratio of thewear volume of SS400 and the wear volume of an alloy to be compared,based upon that of mild steel SS400 as a reference value.

The target wear-resistant property of the developed alloy was awear-resistant property obtained when stellite No. 1 alloy wasgas-welded, and the wear coefficient was WR=8. The cladding method forthe stellite alloy is normally carried out by a gas welding in the caseof a cladding process of a small object, while in the case of a claddingprocess for a member having a large area, an arc welding method is usedfor the cladding process. The arc welding method has a higher weldingefficiency in comparison with the gas welding, and its claddingtechnique is easier than that of the gas welding, and in recent years,welding technicians are well skilled in the arc welding; however, thegreatest defect in the cladding process by the arc welding is that themelt-in depth in the base material becomes greater to cause seriousdegradation of the wear-resistant property.

In the case where stellite No. 1 is subjected to a cladding process bythe TIG method, the wear coefficient becomes 54, and without carryingout cladding processes of two to three layers, a wear-resistant propertyequivalent to that of the gas method is not obtained. Moreover, the wearcoefficient of high-chromium cast iron is 14 to 17.5, and since the wearcoefficient of a high carbon-high chromium cast-iron-type welding rod isin a range of about 4 to 10, the wear coefficient 14 of stellite No. 6is set as a lowest target value, with the true target value being set toWR=8 of the gas welding of stellite No. 1. The appropriate range of thewear coefficient WR of the developed alloy is set in a range of 1≦WR≦15.

(8) Evaluation on Bending Process Performance and Wear-ResistantProperty of Clad Welding Material

Evaluations on the bending process performance and wear-resistantproperty of a welding material is basically matched to the correlationformula of Si×B and Cr obtained in the wear-resistant steel plate.Different points of cast steel from the wear-resistant steel plate arethat the dilution rate due to the base material is different and thatthe bending process is not particularly required. Therefore, a slightlylarger amount of added alloys is permissible in comparison with theproduction of the wear-resistant steel plate.

With respect to the added component range in the welding material, it isnecessary to correct components obtained in a clad steel plate sincethere are big variations depending on the clad welding methods, thekinds of base materials and melting-in depths. For example, in the caseof a cladding operation of a hand welding rod, a melting-in rate ofabout 50% is expected, that of about 35% is expected in the MIG welding,that of about 45% is expected in the TIG welding, that of about 35% isexpected in a flux cored wire, and that of 30 to 60% is expected in asubmerged arc method. In general, since the welding material is easilyinfluenced by considerably deep melting-in, a larger amount of additionis required in comparison with the amount of addition upon producing aclad steel plate. Here, it is assumed that in the case of a clad steelplate, the melting-in depth is in a range from about 25 to 35%.

A different point of the clad welding material from the clad steel plateis that the necessity of bending processes is very small. Originally,since a cladding process is carried out on the surface of an articleformed into an original shape, it is not necessary to carry out abending process. However, in the case of the clad welding, claddingprocesses are carried out in a manner so as to laminate layers, such asa first layer, a second layer and on the like, so that as the number oflayers increases, effects from the base material dilution are reducedand the resulting components come to approximate to designed components.In general, a two-layer cladding process is often carried out, andgenerally, the thickness of the first layer is set to about 3 mm, andthat of the second layer is set to 5 to 6 mm. In the case where layersthe number of which is more than two are deposited, the amount of use ofthe welding material increases, and the number of cladding processes isalso increased, resulting in high costs; therefore, a generally-usedmethod carries out two-layer cladding processes.

As a result of examinations on the respective alloy components to beadded to the welding material, the carbon content is set to 0.5%≦C≦2.5%,the chromium content is set to 15%≦Cr≦45%, and 0≦Ni≦13%, 0≦Mn≦10% and0≦Nb+V≦8% are set, while Cu: 7% or less and Mo: 10% or less are set;thus, sufficient performances can be maintained within these ranges,even when subjected to melting-in effects.

Here, B, which gives great influences to the bending processperformances, was set from 0.5% to 4.5%, and Si was set from 2.5% to5.5%. In particular, the maximum added amount of Si, which givesinfluences to the bending process performances, could be made 1.5% lessthan that of U.S. Pat. No. 3,343,576. That is, since the presentdeveloped alloy is not an alloy developed so as to be used forhigh-temperature applications of 600° C. or more, it is not necessary todeposit needle-shaped carbides so that it becomes possible to reduce theadded amount of Si that directly relates to the precipitation ofneedle-shaped carbides.

By appropriately combining four elements, Cr, Si, B and Nb, it becamepossible to ensure a bending process performance (ductility), the targetwear-resistant property and corrosion-resistant property at normaltemperature in the present developed alloy.

Table 7 shows the hardness and wear-resistant property of each ofvarious typical alloys so as to be compared with one another. Each ofSS400 and SUS310S stainless steels, high chromium cast iron and sulfuricacid resistant steel plate was cut out from a base material, and each ofstellite No. 1 and stellite No. 6 was cladded thereon by a two-layer gaswelding method with a thickness of 5 mm, and each of GL and UF wascladded thereon by a non-gas arc method as two layers having a thicknessof 5 mm.

The alloy of the wear-resistant steel plate was cladded by a submergedarc method as one layer with a thickness of about 5 mm. The basematerials of cladded products were SS400, SUS304 and SUS310S stainlesssteels, each having a thickness of 9 mm.

TABLE 7 Comparative table between hardness and wear-resistant propertyof various typical alloys Main chemical component % Applied base WearMaterial by weight material Hardness coefficient SS400 C—Mn—P < 0.050Material HV160 100 S < 0.050, residual Fe SUS310S C < 0.08, Cr24 to 26,Material HV184 85.0 Ni19 to 22, residual Fe High-chromium C < 3, Cr26 to30, Material HV544 to 700 14 to cast iron residual Fe 17.5 Sulfuric acidC0.04, Si0.1, Mn0.1, Material HV146 105 resistant Cu0.3, residual Festeel plate Stellite No. 1 C2.5, Cr32, Ni1.7, Cladding HV838 8.0 W12,Fe2, residual Co material Gas method Stellite No. 6 C1.2, Cr27, Ni2.7Cladding HV659 14.0 W4.6, Fe2.4, residual Co material Gas method GLC5.3, Cr32, residual Fe Cladding HV766 6.0 material UF C5.8, Cr21, Mo6,W2.5, Cladding HV970 2.0 V1.2, Nb6, residual Fe material

The present invention has been devised based upon the above-mentionedfindings, and the iron-based corrosion-resistant and wear-resistant cladwelding material contains, all percentages by weight, C: 0.5 to 2.5%,Si: 2.5 to 5.5%, Mn: 0 to 10% or less, Cr: 15% to 45%, Ni: 0 to 13%, Cu:7% or less, Mo: 10% or less, B: 0.5% to 4.5%, and 0≦Nb+V≦8%, withremaining portions being composed of iron and incidental impurities.

In addition to these components, the clad welding material can includeone kind or two or more kinds of Ti: 1.0% or less, Al: 3% or less, rareearth metals: 0.5% or less in total, and N: 0.2% or less.

The welding material is provided as a coated arc welding rod, a fluxcored complex wire, a metallic powder or a cast rod.

Moreover, the iron-based corrosion-resistant and wear-resistant alloy ofthe present invention is a low carbon-high silicon-highchromium—boron-niobium-type iron-based corrosion-resistant andwear-resistant alloy that contains, all percentages by weight, C: 0.5 to2.5% by weight, Si: 2.5 to 4.5%, Mn: 0 to 10% or less, Cr: 15% to 31%,Ni: 0 to 16%, Cu: 7% or less, Mo: 10% or less, B: 0.5% to 3.5%, and0≦Nb+V≦8%, and in this arrangement, within a range of 15%≦Cr<27%, (Si×B)2014/Cr²+0.083Cr+1.05 is satisfied, within a range of 27%≦Cr≦31%,1.25%≦(Si×B)≦6.0% is satisfied, within a range of 15%≦Cr<20%,(Si×B)≧570/Cr²−0.066Cr+1.145 is satisfied, and within a range of20%≦Cr≦31%, (Si×B)≧1.25 is satisfied.

In addition to these components, the alloy can include one kind or twoor more kinds of Ti: 1.0% or less, Al: 3% or less, rare earth metals:0.5% or less in total, and N: 0.2% or less.

This iron-based corrosion-resistant and wear-resistant alloy is morespecifically a clad welding metal or cast steel that has awear-resistant property and a corrosion-resistant property that are thesame as, or superior to those of cobalt-based alloys, stellites No. 1and No. 6 that are.

The functions of the respective elements forming the material of thepresent invention and the alloy of the present invention are explainedbelow:

C: 0.5 to 2.5% (material), 0.5 to 2.0% (alloy)

In the case of 0.5% or less of the amount of C, the amount ofprecipitation of chromium carbides contributing to the wear-resistantproperty is lowered. In the case of 3% or more of the amount of C, (Cr,Fe)₇C₃-type carbides are precipitated as needle-shaped carbides formedinto roughened grains to cause peeling and brittleness of the claddingmetal, resulting in degradation of the processability. In the case ofthe wear-resistant steel plate, since bending processability isrequired, the carbon content contained in the deposited metal ispreferably set to 2% or less. Determining from the iron-carbon statediagram, the content 2% or less forms a transition point where cast ironis converted to cast steel so that the cast steel becomes richer thanthe cast iron in its ductility. The clad welding is influenced bymelting-in to the base material metal, and even when 2.5% of C is addedto the alloy material, the carbon content of the first layer depositedmetal is lowered to about 1.5 to 1.9% upon receipt of a base materialdilution of 25 to 40%. Therefore, the amount of carbon to be added tothe alloy is set to 2.5% or less even in the maximum.

Moreover, the amount of carbon contained in the deposited metal givesinfluences to the corrosion-resistant property, and the addition thereofin a range of 0.5% to 3.0% does not cause much influences to corrosionrelating to a 10% hydrochloric acid solution; however, the additionthereof exceeding 2.0% causes an abrupt reduction in thecorrosion-resistant property against corrosion caused by a 10% sulfuricacid solution. Although the amount thereof in a range from 0.5% to 1.5%does not cause any change in the corrosive weight reduction, an abruptchange occurs when the amount thereof becomes 2.0%.

In particular, with respect to a desirable amount of the carbonaddition, the lower limit is preferably set to 0.5% or more, anddetermining from the sulfuric acid corrosion-resistant property, theupper limit is preferably set to 2.0% or less, and is more preferablyset to 2.5% or less even in the maximum, when taken into considerationeffects of the melting-in depths derived from various kinds of weldingmethods.

Si: 2.5 to 5.5 (material), 2.5% to 4.5% (alloy)

Here, Si has a function for preventing oxidation of the steel. Theamount of Si addition of 2.5% or more increases an oxidation resistance,and the amount of Si addition alone of 5% or more effectively preventsoxidation in a temperature range up to 1100° C. From the viewpoint ofcorrosion-resistant property, Si is effective to the hydrochloric acidcorrosion-resistant property and sulfuric acid corrosion-resistantproperty, and the real merit is exerted when it coexists with Cr, Mo andCu.

However, a high Si-content causes brittleness of the steel, and a largeamount of addition thereof makes the steel vulnerable to surface layerpeeling, and, in particular, gives adverse effects to the bendingprocessability of a wear-resistant steel plate; therefore, the minimumamount of addition was set to 2.5%. The amount less than this causesdegradation of the wear-resistant property and corrosion-resistantproperty, and simultaneously gives adverse effects to the hydrochloricacid corrosion resistance.

Here, Si exceeding 4.5% causes serious brittleness to the steel and thesubsequent degradation of ductility of the steel, with the result thatslice-shaped peeling occur on the surface layer face, with claddedportions remaining thereon. Moreover, this gives adverse effects to thebending processability so that this value is set as the upper limitvalue of the maximum amount of addition. Furthermore, when Si exceeds4.5%, with the Cr content being 30% or more, a large amount ofneedle-shaped chromium carbides are precipitated to cause brittleness.In particular, with respect to the amount of Si addition, the lowerlimit is preferably set to 2.5% or more, and determining from thesulfuric acid corrosion-resistant property, the upper limit ispreferably set to 5.5% or less even in the maximum, when taken intoconsideration effects of the melting-in depths derived from variouskinds of welding methods, and in particular, the upper limit is morepreferably set to 4.5% or less.

As the Si content is increased with the Cr content being made constant,the resulting hardened metal becomes brittle in proportion thereto.Therefore, the Si content is made as low as possible within theessential range of 2.5%≦Si≦4.5% so as to prevent brittleness. Since thewear-resistant property is lowered in response to the reduction of Si,the lowered wear-resistant property is recovered by adding B, Nb, V andthe like thereto so as to coexist. In this case, the shapes of borides,niobium and vanadium carbides need to be formed into a spherical shape,in the same manner as in spherical graphite grains of ductile cast iron,so as to physically improve the fracture toughness of the alloy, andthis arrangement forms the best means for ensuring the ductility of thehigh Si-containing steel.

Cr: 15% to 45% (material), 15% to 31% (alloy)

Generally speaking, Cr is very effective to suppress oxidation of thesteel, and contributes to improvements of high-temperature oxidationresistant property. Here, Cr combines with carbon to deposit variouskinds of chromium carbides to provide high hardness so that thewear-resistant property of the steel is improved. However, in order toimprove the wear-resistant property, carbon needs to be combined with Crto form chromium carbides, and for this reason, a large amount of carbonshould be added. However, in the case of the amount of carbon additionof less than 3%, the first layer deposited metal is made to have acarbon content of about 2% when subjected to the base material dilution,with the result that a sufficient precipitation of carbides is notexpected to cause degradation of the wear-resistant property; incontrast, the corrosion resistant property is improved. In order toimprove the corrosion-resistant property of an iron-based alloy that isthe main objective of the present invention, the precipitation of alarge amount of carbides is suppressed so that the carbides are allowedto remain in the matrix.

The corrosion-resistant property is improved by increasing the amount ofCr, while the wear-resistant property is improved by adding thereto B,Nb and Si that give no adverse effects to the corrosion-resistantproperty, so that the amount of addition of C is suppressed to 2.5% orless. Moreover, with respect to the alloy of the present invention, oneof the major objectives of the claims of the present invention is toprovide ductility to the high Si-containing steel, and the Cr contentgives great influences to the ductility of the high Si-containing steel.The correlation between the Cr content and the product of Si and B hasbeen already explained in detail.

Since the clad welding process is carried out on a different kind ofbase metal, it is subjected to dilution from the base material metal. Inthe present invention, the chromium content of the first layer depositedmetal obtained by receiving the base material dilution is set to 15% asthe minimum value, while it is also set to 31% as the maximum value.Therefore, since different dilution rates are caused by base metalsdepending on various kinds of different cladding methods, the minimumrate of addition is set to 15%, and the maximum rate of addition is setto 45%.

In the case of a high Cr-content of 25% or more, brittle needle-shapedcarbides tend to be precipitated depending on combinations with S, andin the case where the alloy is subjected to impact wear due to theapplication thereof, and calls for ductility, a low Cr-content steel inwhich needle-shaped carbides are hardly precipitated is selected sothat, for example, a 15% chromium steel is desirably used. With respectto desirable Cr values, the lower limit is set to 15% or more, and theupper limit is set to 31% or less.

Mn: 0 to 10% (material, alloy)

Mn and Ni accelerate austenitizing to increase its stability. Theaustenite-forming capability of Mn is about half that of Ni. Mn has aneffect for stabilizing the processability of a clad welding operation.Since the alloy of the present invention has a high Si-content as itsbasic composition, ferrites are contained therein, and in order tomaintain the austenite texture, Mn is added thereto in place of Nibecause Ni is expensive. In particular, a desirable amount of Mnaddition is set from 0% to 8% or less as its upper limit.

Ni: 0 to 13% (material) 0 to 16% (alloy)

Determining from the purpose of the present invention, a high amount ofNi addition is not desirable from the viewpoint of consumption of ararity-value alloy, and 0% is preferable. Therefore, Ni is unavoidablyused only when the addition thereof is required for maintaining thewear-resistant property and bending process ductility. In the case ofthe Cr content from 23.5% or more to 31% or less, when the Ni contentincreases by 3 to 6%, the bending ductility is improved or the tendencyof surface layer face peeling is reduced so that an effect for improvingthe Si×B value by 3 points is confirmed. The alloy of the presentinvention is applied to refuse burning facilities in many cases, and ahigh Ni-content is desirable so as to effectively improve a chlorine gascorrosion-resistant property. This is also effective for preventingcarburization at high temperatures, and also has an effect forpreventing peeling of a passive-state coat film of Cr in the applicationvulnerable to a thermal shock; therefore, a high Ni-content is desirablyapplied for use at high temperatures.

Basically, the alloy texture of the present invention easily forms aferrite+austenite mixed texture, and by the use of a joined addition ofMn and Ni, the texture can be converted into an austenite texture. Forexample, in the case where, upon carrying out a hardened claddingprocess on an austenite stainless steel heavily constrained, the presentdevice is subjected to a thermal shock due to serious temperaturechanges, a stress tends to appear on a welding fusion line due to adifference in linear expansion coefficients from the base materialaustenite stainless steel to cause a possibility of peeling when a largeamount of ferrites are contained in the hardened cladding metal. In thiscase, by adding Ni thereto, the hardened metal can be changed into anaustenite simple-substance texture so as to be adjusted to the sametexture as that of the base material. For this reason, the maximumamount of Ni addition is preferably set to 13% or less. If the additionshould be insufficient, Mn may be added so as to be adjusted.

Nb+V: 0% or more, 8% or less (material, alloy)

Nb has an effect for finely spherizing carbides so that a physicaltexture that is hardly subjected to fractures and brittleness is formed.As has beer described earlier, this exerts the same effects andfunctions on carbide shapes as those exerted by Ca and Mg so as tospherize graphite in the same manner as in graphite shapes that giveinfluences to the ductility of gray pig iron and ductile cast iron, asdescribed earlier. Moreover, the greatest purpose of the addition isthat the niobium carbides themselves have high hardness, that is, aboutHV2400. In the case of a low carbon content, for example, C=0.7%, withina range where no NbC (niobium carbides) is crystallized, high-hardnessNbB (niobium boride, Hv2250) is crystallized in place thereof so that itbecomes possible to prevent degradation of the wear-resistant property.

Here, V forms fine carbides, and its forming capability is locatedbetween those of Cr and Mo, and this carbide reaction provides atempering resistance and improvements of secondary hardening by thetempering so that the high-temperature wear resistance can be improved.Moreover, the resistance against cracks is improved by softeningdeformation and heat checking caused by a temperature rise.

In the case of such a high Si×B value as to cause peeling and drops-offin the deposited metal in the correlation formula of Cr content andSi×B, that is, in a limited state where no bending ductility isavailable, it is not necessarily required to add these elements. Theaddition further accelerates brittleness of the deposited metal. Fromthe viewpoint of preventing grain interface corrosicn of a 15%low-chromium content steel, the addition of at least Nb+V≧0.5% ispreferably carried out. Therefore, the amount of addition is set to 0%or more, preferably, to 0.5% or more. However, since the addition of 8%or more in the total saturates the effect thereof, and causes apossibility of causing brittleness of the cladding metal, the maximumamount of addition is set to 8% in the total.

B: 0.5% to 4.5% (material, 0.5% to 3.5% (alloy)

Some of borides to be crystallized in the alloy component range of thepresent invention have such shapes as not to accelerate brittleness ofthe alloy, and, for example, Mo₂FeB₂ has a network shape, NbB has anindefinite shape, and Cr₂B has a plate shape. The respective microhardnesses are HV2400, HV2250 and HV1400, which are very hard. Here,Cr₂B is crystallized with a plate shape, and the resulting crystallizedmatters include bigger ones in comparison with needle-shaped chromiumcarbides; however, the number of them is small, and most of them haveshort lengths and are discontinuous, and although they have problemswith shapes, they cause less possibility of making the matrix physicallybrittle as long as they are not continuously crystallized. This isproved by the fact that, even after a 200R bending process has beencarried out, the resulting hardened metal is very normal without havingeven small pieces of peeling. In order to obtain these effects, theamount of B addition is set from 0.5% in the minimum amount of additionto 3.5% in the maximum amount of addition, and when taken intoconsideration effects of the melting-in depths derived from variouskinds of welding methods, the maximum amount of addition is set to 4.5%or less with respect to the welding material.

Ti: 1.0% or less (material, alloy)

Titanium carbides also provide extremely high hardness; however,titanium impairs welding operability, failing to finish the bead surfaceflatly. Therefore, in the same manner as in Nb, the amount of additionthereof is set to 1% or less in the maximum, from the viewpoint ofpreventing grain interface corrosion of a 15% low-chromium contentsteel. Al: 3% or less, N: 0.2%, rare earth metals, such as Ce and Y:0.5% in the total amount of one kind or two or more kinds

The alloy of the present invention may be used for applications rangingfrom normal temperature to a high temperature of 600° C. or more, andneeds to be provided with a high-temperature oxidation resistantproperty. These elements can be selectively added so as to mainlyimprove the oxidation resistant property at high temperatures. Forexample, Al improves the oxidation resistant property at hightemperatures, and exerts its effects in particular in the applicationatmosphere including much sulfur gas. In this case, the amount of Ni ispreferably made smaller, while the amount of Al is preferably madegreater. When Al exceeds 3%, an alumina coat film is generated on thecladding metal, with the result that slag is easily included to impairthe welding operability. In order to obtain the effects stably, theamount of addition is preferably set to 0.5% or more to 3% or less.

Mo: 10% or less (material, alloy)

Mo exerts remarkable effects to sulfuric acid corrosion resistance andhydrochloric acid corrosion resistance when added so as to coexist withCr, Cu and Si, and the resulting corrosion-resistant property is thesame as, or more than that of stellites No. 1 and No. 6. that arecobalt-based alloys. However, at present, Mo has become a very expensivealloy, and since an increase of the amount of addition causes an extremerise of the production unit price of the alloy of the present invention,the minimum amount of addition is set to 0%, and the maximum amount ofaddition is set to 10%. In particular, since the amount of addition of8% provides a sulfuric acid resistant property that exceeds theresistant property of the stellite, the further addition causes anexcessive addition so that the maximum amount of addition is set to 10%or less, with the maximum amount of addition being more preferably setto 8%.

Cu: 7% or less (material, alloy)

Cu improves the sulfuric acid resistant property and hydrochloric acidresistant property. In the case where, in a refuse incinerator, aburning process is suspended, highly corrosive acid dew-point solutions,such as sulfuric acid and hydrochloric acid solutions, are generated,and with respect to these, the addition of Mo alone is not so effective,a composite addition with Cu is effectively carried out. Moreover, thecomposite addition miniaturizes the micro texture, thereby allowing fineneedle-shaped carbides to be easily precipitated in a high Cr-contentand high Si-content state so that the high-temperature wear-resistantproperty is improved.

With respect to the base material metal, irrespective of the kindsthereof, in particular, for example, easily weldable steels, such asmild steel, weather-resistant steel plates, sulfuric acid resistantsteel, sea-water resistant steel, various stainless steels, Mn—Craustenite steel, nickel alloy steel, chromium alloy steel and the like,may be used, and from the viewpoints of suppressing dilution and ofensuring the corrosion-resistant property and high-temperature oxidationresistant property, those containing Cr in a range of 9 to 35% and Ni ina range of 0 to 25% are preferably used.

EFFECTS OF THE INVENTION

The iron-based corrosion-resistant and wear-resistant metal is anepoch-making alloy which, although produced as an inexpensive iron-basedalloy, endures sulfuric acid corrosion and hydrochloric acid corrosionas an alternative metal for expensive cobalt-based alloy andnickel-based alloy, also has a wear-resistant property that is the sameas, or superior to that of these alloys, and is applicable as variouswelding materials, wear-resistant steel plates and cast steel.

From the world-wide viewpoint, at present, enormous amounts of expensiverarity-value alloys, such as cobalt and nickel, have been consumed asalloys for use as simply wear-resistant clad welding materials forproduction facilities, and worn and lost, dispersion-consumed, anddiscarded without being recovered in all over the world. In thefuture-oriented standpoint, the current wasteful consumptions of theserarity-value alloys will lead to lack of resources in the nextgenerations sooner or later, and from now, effective utilizations ofrare alloys and improvements of the resource-recovering efficiency haveto be taken into consideration. Therefore, from the standpoint ofeffective utilizations of resources, the present inventors have proposedthe utilization of silicon that has enormous amounts of deposits on theearth and is inexpensive since 26 years ago, and have continuouslystudied its application to clad welding materials as one of effectiveutilizations thereof.

At that time, an SLCE alloy having added amounts of alloy elements of C:5.2%, Si: 12.3% and Cr: 20% (wear coefficient WR=7, average hardnessHV=730) was developed, and a wear-resistant steel plate was produced.Many of this were supplied to copper refining factories,paper-manufacturing companies and cement companies, and were alsoexported to a paper-manufacturing company in Sweden. Although this alloyis strong against hydrochloric acid corrosion and sulfuric acidcorrosion, and considerable evaluations were obtained; however, thealloy was poor in processability in a bending process or the like, andhad a very brittle characteristic.

When Si was added to metal as an alloy, brittleness that was inherent toSi was caused, in particular, in an inexpensive iron-based alloy, makingit very difficult to practically apply this as a welding material. Inparticular, this was characterized by the fact that innumerable crackswere caused in the thickness direction of the deposited metal. Becauseof its brittleness, slice-shaped peeling occur on the surface layer faceof the clad welding metal and lump-shaped drops-off are generated fromthe base metal as the content thereof increases. Moreover, in the caseof a wear-resistant steel plate, even upon applying a pressure by usinga press or the like in a distortion removing process, peeling anddrops-off occur, thereby limiting the application thereof to restrictedusages. In the case where applied as a clad welding wire and a weldingrod, even upon application of a slight impact to the cladded matter,peeling and drops-off occurred in the hardened clad welding metal.

After having studied for long years, the present inventors have given upthe idea of applying Si alone, and succeeded in revising its brittlenessby adding elements such as B, Nb and V so as to coexist therewith; thus,the present invention has been completed. In this method, although it isnot possible to prevent Si from causing brittleness to an iron-basedalloy, by using the characteristic that, when Si increases, Si formschromium carbides in a high chromium-content steel into a needle-shape,niobium that forms niobium carbides that are miniaturized into sphericalshapes or boron that allows plate-shaped borides having a net-workshape, an indefinite shape or a plate shape to be crystallized are addedin order to suppress the amount of precipitation of needle-shapedcarbides and also to compensate for the reduced portion; thus, thebrittleness is suppressed and the wear-resistant property is improved.In particular, Nb is a very effective alloy element as an alloy thatexpands the adjusting range of the wear-resistant property so as toadjust the wear-resistant property.

BEST MODE FOR CARRYING OUT THE INVENTION

The following description will discuss embodiments of the presentinvention.

Tables 8 to 10 show compositions of deposited metals of various kinds ofwear-resistant steel plates that were produced so as to obtain acorrelation formula between Si×B and Cr.

TABLE 8 Added chemical components (% by weight) to fused metals ofwear-resistant steel plates TP. C Si Ni Cr Mo Nb B Cu  1 1.5 4.0 3.320.0 4.5 2.0 3.0 4.6  2 1.5 3.5 3.3 20.0 4.5 2.0 3.0 4.6  3 1.5 3.5 3.320.0 4.5 2.0 2.3 4.6  4 1.5 3.5 3.3 20.0 4.5 3.0 1.6 4.6  5-C 1.5 2.53.3 13.0 4.5 4.0 1.0 4.6  6, 19 0.7 2.6 3.3 25.0 4.7 0.5 2.5 4.6  7, 200.7 2.5 3.3 27.0 4.6 3.0 1.7 4.5  8 2.5 2.6 3.3 25.0 4.6 6.0 1.0 4.6  9,22 1.5 3.5 10.0 25.0 4.6 4.0 0.5 4.6 10 0.7 3.6 3.3 27.0 4.6 0.5 2.4 4.511 1.4 5.0 3.3 29.0 4.4 0.5 1.7 4.6 12 0.5 4.0 3.6 29.0 4.6 0.5 1.7 4.613 1.5 3.5 3.3 30.0 4.6 4.0 0.5 4.6 14 3.0 4.1 3.3 32.0 0 6.0 1.8 3.5 150.7 3.7 3.3 26.0 4.6 4.0 1.7 4.5 16 2.0 3.1 3.3 32.0 0 6.0 1.8 3.5 171.5 3.6 3.3 31.0 4.6 4.0 1.0 4.6 18 1.5 2.6 3.3 25.0 4.6 0.5 3.0 4.618-1 1.5 2.6 0 27.5 4.6 0.5 3.0 4.6 19-1 0.7 2.6 0 27.5 4.6 0.5 2.5 4.621 1.5 2.5 0 27.0 4.5 8.1 1.0 4.6 23 1.5 3.5 0 31.0 4.5 2.0 2.4 4.6 241.5 2.5 3.3 28.0 4.5 4.0 0.5 4.6 25 1.5 3.5 0 32.0 4.5 2.0 2.3 4.6 262.5 3.1 3.3 25.0 0 6.0 1.5 3.5 27 1.5 2.5 3.3 32.0 4.6 4.0 1.0 4.6

TABLE 9 28 1.5 3.5 3.3 24.0 4.6 6.0 0.5 4.6 Mn8 29 1.5 3.5 3.3 25.0 8.16.0 0.5 4.6 30 1.5 3.5 3.3 25.0 4.6 6.0 0.5 6.0 31 2.0 3.5 0 29.0 0 0.52.1 4.6 31-1 2.0 3.5 0 31.5 0 0.5 2.1 4.6 32 2.0 3.5 0 29.0 0 2.0 1.64.6 32-1 2.0 3.5 0 31.5 0 2.0 1.6 4.6 33 2.0 3.5 0 29.0 0 4.0 1.0 4.6 342.0 3.5 0 33.0 0 2.0 1.6 3.5 35AL 1.5 3.5 AL2 23.0 0 4.0 0.5 4.6 36 1.54.0 0 25.0 4.5 0.5 2.5 4.6 37 3.0 4.0 0 23.0 0 0.5 2.1 3.5 38 2.0 4.0 029.0 0 0.5 2.1 4.6 39 5.5 4.0 0 22.0 0 6.0 0 3.3 40 3.0 4.0 3.3 32.0 00.5 1.7 4.6 41 2.0 5.0 3.3 30.0 4.6 0 0 4.6 42 3.0 5.1 3.3 30.0 4.6 0 04.6 43 3.0 4.0 0 30.0 0 3.1 1.6 3.5 44 3.0 4.0 0 34.0 0 3.1 1.6 3.5 451.5 4.0 9 25.0 4.5 0.5 2.5 4.6 46 1.5 3.5 6 24.0 4.5 0.5 3.0 4.5 47 2.53.0 8 25.0 0 0.5 3.0 4.5 48 0.7 3.5 3.3 30.0 4.6 V2.0 1.7 4.6 49 1.5 3.53.3 31.0 4.6 V4.0 0.5 4.6 50 0.7 2.5 3.3 27.0 4.6 V2.0 1.7 4.6 51 0.54.0 3.3 30.0 0 0 0 4.7 52 1.5 4.0 3.3 30.0 0 0 0 4.7 53 2.5 4.0 3.3 30.00 0 0 4.7 54 3.0 4.0 3.3 30.0 Mn4 0 0 4.7 55 1.5 4.0 3.7 36.0 Mn4 0 0 056 1.3 4.5 3.7 20.0 Mn3.5 0 0 0 57 1.3 4.5 3.7 20.0 Mn3.6 0.6 1.0 0 581.3 4.5 3.7 20.0 Mn3.6 0.5 2.0 0

TABLE 10 59 1.5 3.5 0 20.0 4.6 V8.0 0.5 4.6 60 1.5 3.5 0 20.0 4.6 V6.00.5 4.6 61 0.7 2.5 0 20.0 4.6 V6.0 1.7 4.6 62 2.0 2.6 3.3 25.0 4.6 6.01.0 4.6 63 2.0 4.0 3.3 31.0 0 6.0 1.8 4.6 64 2.0 3.2 3.3 25.0 0 6.0 1.53.5 65 2.0 4.1 0 24.0 0 0.5 2.1 3.5 66 1.5 2.5 3.3 13.0 4.5 4.0 3.5 4.667 1.5 2.5 3.3 18.0 4.5 0.5 3.5 4.6 68 1.5 2.5 3.3 20.0 4.5 0.5 3.0 4.669 1.3 4.5 3.7 20.0 Mn3.6 8.0 0 0 70 1.3 4.5 3.7 25.0 Mn3.6 8.0 0 0 712.0 4.1 3.3 30.0 0 0 0 4.7 72 1.5 2.5 3.3 26.0 4.5 0.5 2.7 4.6

The bending processability of each of these wear-resistant steel plateswas examined. The content of Cr contained in the first layer depositedmetal was calculated with a base-material dilution ratio being set to25%. As described earlier, the evaluation of the bending processabilityof the deposited metal was carried out by using the following method inwhich a clad steel plate that was cladded with deposited metal with athickness of 5 to 6 mm with a single cladded layer over the entiresurface of each of steel plates having a size of 9 mm in massthickness×100 mm in width×400 mm in length of SS400, SUS400, SUS304 andSUS310S was produced, and this was subjected to a bending process by apress with the hardened metal placed on the inner side. A stellite No. 1alloy, which was a target material, was cladded on SS400 with two layershaving a thickness of 5 mm, by a gas welding process. The length of eachsample piece was set to about 200 mm.

The bending curvature was set to about 200R, and the flextural ductilitywas evaluated in the following three-degree criteria: in the case whereno influences were caused on the hardened metal by the bending and anappropriate bending performance was obtained without causing anydefects, this state was evaluated as ◯, in the case where severalsurface-layer peeling and extremely slight cracks occurred on thesurface of the hardened metal, this state was evaluated as , and in thecase where many surface-layer peeling and lamp-shaped cracks occurred tocause poor toughness, this state was evaluated as . The results areshown in the following Tables.

TABLE 11 Influences of Si × B to bending processability ofwear-resistant steel plate Amount of Cr contained in the first-layerfused metal (not the amount of addition, with a base material dilutionratio being set to 25%) Si × B round off to the nearest Hard- wholeBending Base ness TP C Si Cr Nb number ductility material HV WR  1 1.54.0 15.0 2.0 12  SS 806 2.2  2 1.5 3.5 15.0 2.0 10.5 ◯ SS 758 4.0  31.5 3.5 15.0 2.0 8.1 ◯ SS 746 9.6  4 1.5 3.5 15.0 3.0 5.6 ◯ SS 618 9.1 5-C 1.5 2.5 16.0 4.0 2.5 ◯ 310 360 15.0  6 0.7 2.6 19.0 0.5 6.5 ◯ SS615 5.6  7 0.7 2.5 20.0 3.0 4.3 ◯ SS 533 11.0  8 2.5 2.6 19.0 6.0 2.6 ◯SS 680 4.0  9 1.5 3.5 19.0 4.0 1.8 ◯ SS 404 11.0 10 0.7 3.6 20.0 0.5 8.6 SS 655 3.3 10-C 27.0 ◯ 310 595 4.1 11 1.4 5.0 22.0 0.5 8.5  SS 8182.0 12 0.5 4.0 22.0 0.5 7.0 ◯ SS 563 7.4 13 1.5 3.5 23.0 4.0 1.8 ◯ SS744 9.0 14 3.0 4.1 24.0 6.0 7.4  SS 712 2.0 14-C 30.0  310 747 2.3 150.7 3.7 24.0 4.0 6.3  304 662 5.0

TABLE 12 16 2.0 3.1 24.0 6.0 5.6 ◯ SS 624 4.0 16-C 30.0 ▴ 310 622 4.8 171.5 3.6 23.0 4.0 3.6 ▴ SS 780 3.3 17-C 30.0 ◯ 310 18 1.5 2.6 25.0 0.57.8 ◯ 310 482 4.5 18-1 1.5 2.6 25.0 0.5 7.8  304 — — 19 0.7 2.6 25.00.5 6.5 ◯ 310 501 4.1 19-1 0.7 2.6 25.0 0.5 6.5 ▴ 304 — 5.6 20 0.7 2.525.0 3.0 4.3 ◯ 310 405 12.6 21 1.5 2.5 25.0 8.1 2.5 ◯ 304 547 11.0 221.5 3.5 25.0 4.0 1.8 ◯ 310 358 11.3 23 1.5 3.5 30.0 2.0 8.4 ◯ 310 6583.6 24 1.5 2.5 27.0 4.0 1.3 ◯ 310 402 14.0 25 1.5 3.5 30.0 2.0 8.1 ▴ 310665 6.3 26 2.5 3.1 23.0 6.0 4.7 ◯ 304 666 3.9 27 1.5 2.5 30.0 4.0 2.5 ◯310 596 8.7 28 1.5 3.5 23.0 6.0 1.8 ◯ 304 483 8.0 29 1.5 3.5 23.0 6.01.8 ◯ 304 621 9.3 30 1.5 3.5 23.0 6.0 1.8 ◯ 304 512 10.0

TABLE 13 Bending Base TP No C Si Cr Nb Si × B ductility materialHardness WR 31 2.0 3.5 28.0 0.5 7.4 ◯ 310 587 4.9 31-1 2.0 3.5 28.0 0.57.4  304 — — 32 2.0 3.5 28.0 2.0 5.6 ◯ 310 551 3.8 32-1 2.0 3.5 28.02.0 5.6 ◯ 304 — — 33 2.0 3.5 28.0 4.0 3.5 ◯ 310 504 5.9 34 2.0 3.5 31.02.0 5.6 ◯ 310 560 5.3 35 1.5 3.5 22.0 4.0 1.8 ◯ 304 528 9.3 AL2. 0 361.5 4.0 19 0.5 10.0  SS 696 4.0 37 3.0 4.0 24 0.5 8.4 ◯ 310 558 5.3 382.0 4.0 28 0.5 8.4 ◯ 310 699 2.8 ⊙39    5.4 4.0 16.0 6.4 0  SS 852 2.0Base material 310 for use in corrosion test 310 862 2.7 Cr = 23%, SS:bending test 40 3.0 4.0 24.0 0.5 6.8  SS 814 2.4 41 2.0 5.0 23.0 0 0 ▴SS 616 6.3 42 3.0 5.0 23.0 0 0  SS 679 2.5 43 3.0 4.0 27.0 3.0 6.0 304 706 3.0 44 3.0 4.0 30.0 3.0 6.0  304 739 3.0

TABLE 14 45 1.5 4.0 19.0 0.5 10.0  SS 713 1.8 46 1.5 3.5 22.0 0.5 10.5 304 608 6.7 47 2.5 3.0 23.0 0.5 9.0  304 622 2.8 48 0.7 3.5 23.0 V2.06.0 ▴ SS 488 16.0 49 1.5 3.5 24.0 V4.0 1.8 ◯ SS 569 19.0 50 0.7 2.5 20.0V2.0 4.3 ◯ SS 589 7.4 51 0.5 4.0 27.0 0 0 ◯ 304 362 99.0 52 1.5 4.0 27.00 0 ◯ 304 385 31.0 53 2.5 4.0 27.0 0 0 ◯ 304 563 5.8 54 3.0 4.0 27.0 0 0◯ 304 597 4.1 55 1.5 4.0 36.0 0 0  310 977 4.2 56 1.3 4.5 20.0 0 0 ◯310 309 77.8 57 1.3 4.5 20.0 0.6 4.5 ◯ 310 351 37.3 58 1.3 4.5 20.0 0.69.0 ◯ 310 427 13.5 59 1.5 3.5 20.0 V8.0 1.8 ◯ 310 479 18.7 60 1.5 3.520.0 V6.0 1.8 ◯ 310 415 22.4 61 0.7 2.5 20.0 V6.0 4.3 ◯ 310 368 14.6 622.0 2.6 19.0 6.0 2.6 ◯ SS 624 6.5

TABLE 15 63 2.0 4.0 24.0 6.0 7.2  SS 640 3.3 63-1 2.0 4.0 30.0 6.0 7.2 310 649 3.6 64 2.0 3.2 23.0 6.0 4.8 ◯ 304 511 12.3 65 2.0 4.1 24.0 0.58.6 ◯ 310 506 8.8 66 1.5 2.5 16.0 4.0 8.8 ◯ 310 583 2.4 67 1.5 2.5 18.00.5 8.8 ◯ 304 618 4.0 68 1.5 2.5 19.5 0.5 7.6 ◯ 304 627 4.8 69 1.3 4.521.0 8.0 0 ◯ 310 335 17.3 70 1.3 4.5 25.0 8.0 0 ◯ 310 362 15.0 71 2.04.1 27.0 0 0 ◯ 304 407 35.6 72 1.5 2.5 19.5 0.5 6.8 ◯ 304 716 6.1

(1) Correlation Between Si×B and Cr

These results are arranged and shown in FIG. 1. In spite of the factthat the amount of carbon addition was extremely reduced to 0.5 to 2.0%within an appropriate range in the correlation graph relating to theproduct of Si×B and Cr content, each of alloys of No. 2, No. 6, No.10-C, No. 15, No. 16, 16-C, No. 23, No. 26, No. 32, No. 32-1, No. 33,No. 34, No. 38, No. 66, No. 67, No. 68 and No. 72 had a wear coefficientin a range of 3 to 6, which indicated that there were many alloys thatcould ensure a wear-resistant property that was about two times or morehigher than that of stellite No. 1 and No. 6.

It is an epoch-making discovery that an wear-resistant property that ishigher than that of high carbon-high chromium cast-iron-type claddingalloy GL (WR=6), and at present, an iron-based high-temperaturewear-resistant clad welding alloy UR (WR=2) has been recognized in theworld as an alloy having the highest wear-resistant property; however,alloys N. 6 and No. 38 ensure a wear-resistant property as high as thewear-resistant property thereof.

In a tendency of the upper limit curve, within the content of Cr betweenabout 15% to about 27%, the numeric value of Si×B dropped from about11.5 to 6, and the numeric value was saturated at about 6, betweenCr=27% or more and Cr=31%. When Si×B exceeds this limit value, thebending performance is extremely lowered to cause peeling and drops-offin the deposited metal itself, resulting in serious degradation in theductility.

As the numeric value of Si×B became higher, the wear resistance wasimproved, and in contrast, as the numeric value of Si×B became lower,the bending performance became better, while the wear resistance waslowered greatly. In order to improve the wear resistance, Nb was addedthereto.

(2) Effects of Addition of Nb

With respect to No. 6 alloy having a Cr content of 19%, a wearcoefficient of WR=5.6 was obtained with Si×B=6.5 and an amount of Nbaddition of 0.5%, and with respect to No. 62 alloy with the same Crcontent, a wear coefficient of WR=6.5 was obtained with Si×B=2.6 and anamount of Nb addition of 6.0%; thus, virtually the same wear resistancewas obtained. In the case where Si×B became a low value of 2.6, the wearcoefficient was lowered to about 9 to 15; however, upon addition of 6%of Nb, the wear coefficient could be recovered up to 6.5.

Thus, Nb exerted capability of positively improving the wear resistance.In the case where the numeric value of Si×B was set within 1.25 to 4.5,the wear coefficient WR tended to be lowered to 8 to 15, that is, aseriously poor level, regardless of the Cr content; however, incontrast, the bending performance was improved. In order to improve thewear resistance within this range, the improvement can be obtained byincreasing or reducing the amount of Nb addition within a range of 4 to8%. In the case where the numeric value of Si×B became 4.5 or more to11.5 or less, by adjusting the amount of Nb addition within 0.5 to 4%,the wear resistance was improved without lowering the bending ductility,and in the case where the numeric value of Si×B became 4.5 or less, byselecting the amount thereof within a range from 4 to 8%, the wearresistance was improved without lowering the bending ductility.

The bending ductility of No. 10 is ; however, since the product of Si×Bis as high as 8.6, the bending ductility can be changed to ◯, byreducing this to about 7. With respect to No. 17 alloy as well, byreducing the amount of Nb addition from 4% to 1 to 2%, the bendingductility can be changed from  to ◯. It is found that by adjusting theamount of Nb addition, as well as by adjusting Si×B, within a rangesurrounded by the upper and lower limit curves, good bending ductilityand superior wear resistance can be obtained.

(2) Effects of V Serving as a Substitution Element for Nb

Normally, it has been said that V and Nb exhibit the same effects asspherical carbide-forming elements; therefore, the effects of V areexamined. In order to examine a difference of effects given by Nb and Vto the wear resistance, a group of Nb alloys and a group of V alloys arecompared with each other. The group of Nb-added alloys are shown inTable 16, while the group of V-added alloys are shown in Table 17.

TABLE 16 Nb-added alloy (Cr: content in the first layer) Bending BaseAlloy C Si Cr Nb Si × B ductility material Hardness WR 7 0.7 2.5 20 34.3 ◯ SS 533 11.0 9 1.5 3.5 19 4 1.8 ◯ SS 404 11.0 20 0.7 2.5 25 3 4.3 ◯310 405 12.6 29 1.5 3.5 23 6 1.8 ◯ 304 621 9.3

TABLE 17 V-added alloy (Cr: content in the first layer) Bending BaseAlloy C Si Cr Nb Si × B ductility material Hardness WR 48 0.7 3.5 23 26.0 ▴ SS 488 16.0 49 1.5 3.5 24 4 1.8 ◯ SS 589 19.0 50 0.7 2.5 20 2 4.3◯ SS 589 7.4 59 1.5 3.5 20 8 1.8 ◯ 310 479 19.0 60 1.5 3.5 20 6 1.8 ◯310 415 22.0 61 0.7 2.5 20 6 4.3 ◯ 310 368 15.0

When Nb alloy No. 7 and V alloy No. 50 were compared with each other,the base material of SS400 was used in both of the alloys, and Si×B=4.3,with the same amounts of addition of C, Cr and Si being used, and Nb=3%and V=2%. The wear coefficient WR was 11.0 for the Nb alloy, and 7.4 forthe V alloy so that the V-added alloy was superior in wear resistance toa certain degree.

When Nb alloy No. 9 and V alloy No. 49 were compared with each other.The amounts of the added alloys were all the same, and the same basematerial of SS400 was used. When the same amount of addition was used,that is, Nb=4% and V=4%, and the former had a wear coefficient WR=11.0and the latter had a wear coefficient WR=19.0; thus, there was adifference between the two values.

In the case of Si×B=4.3, V made it possible to improve the wearresistance better than Nb in spite of the fact that the amount of Vaddition was somewhat smaller than that of Nb. In the case of Si×B=1.8,Nb made it possible to improve the wear resistance overwhelmingly whenthe amounts of addition were the same.

Based upon the comparison tests, it is found that in the case ofSi×B=1.8 that is a low level, the addition of Nb is more effective,while in the case of Si×B=4.3 that is a high level, the addition of V ismore effective to improve the wear resistance even when the amount of Vaddition is smaller than the amount of Nb addition. That is, Vcontributes to improve the wear resistance in the same manner as in Nb.With respect to the bending ductility also, the amount of V addition waslimited to a maximum level of 8% in the same manner as in Nb. Moreover,Nb and V may be added so as to coexist, and the total amount ofadditions of the two materials is preferably set to 8% or less.

(3) Effects of Kinds of Base Materials Given to Wear Resistance

In the case where the content of Cr was in a range from 25% or more to31% or less, more of SUS310S base material was used; however, in thecase of 25% or less, since base materials of mild steel and 304stainless steel were commonly used and subjected to a cladding process,it was feared that the differences in the base materials might causevariations in the wear resistance. The reason for this is because, withrespect to the numeric values of wear coefficients WR indicating wearresistance, the numeric values obtained between the stainless steel basematerial and the mild steel base material were compared with each otherin a mixed mariner. Although originally, the test should be carried outby using the same base material, it cannot help but to use this methodbecause, since the content of chromium in the deposited metal needs tobe varied from 15% to 31%, the adjustment of the content of chromium inthe deposited metal is carried out by utilizing the melting-in of thebase material.

Table 18 shows effects of kinds of base materials that are given to wearresistance. Here, No. 6 alloy and No. 19 alloy had the same amounts ofadded components, and the kind of the base material of the former wasSS400 and that of the latter was SUS310S. In the same manner, withrespect to No. 7 alloy and No. 20 alloy, that of the former was SS400,and that of the latter was SUS310S. With respect to No. 9 alloy and No.22 alloy, that of former was SS400, and that of the latter was 310S.

TABLE 18 Effects of differences of base materials given to wearresistance Kind of base Wear Kind of alloy material Hardness resistanceWR No. 6 SS400 HV615 5.6 No. 19 SUS310S HV501 4.1 No. 7 SS400 HV533 11.0No. 20 SUS310S HV405 12.6 No. 9 SS400 HV404 11.0 No. 22 SUS310S HV35811.3

The factor that was influenced by the differences of the base materialswas the hardness value, and hardly any influences were given to the wearresistance. Since these differences in wear coefficient were includedwithin the scope of claims, no problems were raised. Therefore, it isdetermined that the wear coefficients of SS400 and SUS310S may beregarded as the same.

(4) Relationship Between Ni Content and Bending Ductility

Table 19 shows the relationship between Ni content and bendingprocessability of deposited metal.

TABLE 19 Relationship between nickel content of disposed metal andbending processability Ni content of Difference Alloy Ni added Basedisposed in average Bending number amount material metal value ductilityNo. 18 3.3% 310 7.5% to 5.7% ◯ 8.3% No. 18-1 0.0% 304 2.0% to ▴ 2.4% No.19 3.3% 310 7.5% to 5.7% ◯ 8.3% No. 19-1 0.0% 304 2.0% to ▴ 2.4% No. 310.0% 310 5.0% to 33% ◯ 6.0% No. 31-1 0.0% 304 2.0% to  2.4%

In the case of Cr content from 23 to 24%, stainless steel base materialsSS400 and SUS304 were used, and in the case of Cr content of 25% ormore, stainless steel SUS310S was used. In the case of using SS400 mildsteel base material, the range of the Ni content is set about 0.0 to10%, in the case of using SUS304 base material, it is set about 2.0 to12%, and in the case of SUS310 base material, it is set about 5.0 to16%.

In the case of Cr content from 23.5% or more to 31% or less, when the Nicontent is increased by about 3 to 6%, the bending ductility tends to beimproved by about 3 points in the Si×B value; however, alloys causingcracks also exist in a mixed manner, and in a range surrounded by thisarea, combinations of various elements should be examined carefully, andalloy structures should be made carefully. In the case of Cr content of23.5% or less, the deposited metal causes fractures even when the Nicontent becomes 7 to 8%, failing to obtain a fracture-preventive effectby the Ni addition.

(5) Correlation Formula Between Si×B and Cr Content

1) Upper limit curve under which peeling and drops-off of hardened metalare caused

15% Cr 27%

Si×B≦2014/Cr²+0.083Cr+1.05  (1)

27%≦Cr≦31%

1.25%≦Si×B≦6.0%  (2)

2) Lower limit curve that can keep The wear resistance WR of hardenedmetal at the lowest value of 15

15%≦Cr≦20.0%

Si×B=570/Cr²−0.066Cr+1.145  (3)

20% Cr 31%

Si×B≧1.25  (4)

3) In the case where the Ni content of the deposited metal is increasedby 3 to 6%, with respect to the upper limit curve relating to peelingand drops-off, formula (I) is parallel-shifted upward by a portioncorresponding to Si×B=3 points, in the range from 23.5%≦Cr≦31% so thatthe range that hardly causes cracks is expanded.

(6) Evaluation of Corrosion-Resistant Property of Clad Welding Material

As described earlier, the corrosion-resistant property of the alloy ofthe present invention has been developed for achieving that of Worthitealloy as its target.

The chemical components thereof are explained as follows: C<0.07%,Cr20%, Ni25%, Si3.5%, Mo3.0%, Cu2.0%

In addition to these, DIN8556, E20.25.5LCuR26 may be used as weldingmaterials. The typical chemical components are explained as follows:C0.025%, Mn2%, Si0.4%, Cr21%, Ni25%, Mo5%, Cu1.8%, Nb0.1%, No. 08%

Both of the alloys, which have a high Ni content and are structuralmaterials having a corrosion-resistant property, are not used aswear-resistant metals. The latter is a welding material; however, sinceit has a low Si content, that is, Si=0.4%, with an extremely low carboncontent, it cannot be used as a wear-resistant metal. Therefore, thepresent inventors have set a carbon content required for thewear-resistant metal in a range of 0.5% or more to 2.0% or less.Moreover, since the development of a Si-containing alloy is a mainobjective of the present developed alloy, the SL content is set in arange of 2.5%≦Si≦5.5%. Moreover, in order to improve the wear-resistantproperty, Nb and V, which are carbide-forming elements, are addedthereto, and B, which forms a boride that gives high hardness, is alsoadded so as to co-exist.

An alloy-designing process was carried out so as to modify two kinds ofcorrosion-resistant alloys into a wear-resistant alloy, and also so asnot to impair corrosion-resistant properties that the two kinds of thealloys originally had. Since DIN8556 welding rods are cladded on mildsteel and low alloy steel and used as joining materials andcorrosion-resistant materials for plants in phosphate, sulfate, acetate,salt and sea water environments; however, these are not wear-resistantmaterials, and used for a cladding operation on mechanical structuralmembers.

Alloys, which have a corrosion-resistant property that is superior tothat of stellite No. 1 and stellite No. 6 alloys in the range of thegraph capable of ensuring proper bending ductility andabrasion-resistant property, are invented. Comparison tests forcorrosion-resistant property were carried out on these alloys. In thecorrosion tests, the amount of corrosive reduction of each of these,when immersed into each of a 10% sulfuric acid aqueous solution, a 5%ferrous chloride aqueous solution, a 10% hydrochloric acid aqueoussolution and a 48% caustic soda aqueous solution for 480 hourscontinuously, was measured, and based upon the resulting differences,the superiority and inferiority of the corrosion-resistant property werecompared.

With respect to SS400 mild steel, SUS310S and SUS304 stainless steels,high-chromium cast iron, and sulfuric acid resistant steel, cut pieceswere obtained from a plate member of each of these so that test pieceswere prepared. All the other materials were cladding materials, andcladded on SUS310S steel with a thickness of 5 mm so that test pieceswere prepared. The cladding test pieces were subjected to a corrosivereduction including the base material SUS310S, and using the hardenedmetal obtained by sampling the hardened metal itself for the corrosiontest made it impossible to compare the samples with each other becausemany cracks occurred in some of alloys; therefore, on the assumption ofan actual machine plant, a corrosion test including the base materialwas carried out.

The size of the test piece was set to 50×50 mm, with its thickness beingset to 9 mm. The thickness of the hardened metal was about 5 mm, and thebase material face was ground based upon the hardened metal face so thata thickness of 9 mm was maintained. The entire surface area of the testpiece was 68 cm². The corrosive reduction per unit area was supposed tobe indicated; however, since a different kind of metal SUS310S wasincluded in the base metals, the total corrosive reduction measuredvalues, as they are, are displayed so as to be compared.

The reason that SUS310S is selected as one of the base metals is becausea large amount of chromium can be transferred to the deposited metal asa melting-in portion from the base metal. With this arrangement, theamount of addition of Cr to the deposited metal can be easily adjusted.The amount of chromium content in SUS304 is as small as 18%, and theamount of chromium content in SUS310S is 25% so that this allows a largeamount of chromium to be obtained from the base material metal.Moreover, SUS310S is also superior in corrosion-resistant property. Bythe effect of the melting-in portion, the Cr content of the singlecladded-layer deposited metal becomes the same as, or higher than theadded component, with Cr being picked up from the SUS310S base materialmetal. The melting-in rate of the base material was set to 25%.

In the correlation drawing between Si×B and Cr content in the firstlayer deposited metal, alloys, located in the surrounded area, wereproperly selected, and corrosion tests were carried out thereon. Thosealloys that were subjected to the corrosion tests were surrounded by ◯so as to be easily recognized. Upon using in a high temperature range of800° C., heat resistant stainless steel base materials, such as SUS310and SUS3105, are selected, and plate members to be used as heatresistant materials used from the proximity of room temperature to 800°C., stainless steels, such as SUS304 and SUS316, are mainly used.Therefore, determining from the amount of addition of chromium, the Crcontent of the first layer deposited metal is assumed to be in a rangefrom about 23 to 30%. In the case where the Cr content less than thislevel, mild steel or esten steel is selected as the base material andthe chromium content tends to be lowered in most cases. In the casewhere the corrosion-resistant property is required, at least stainlesssteel is adopted as the base material metal, and steels, such as 304,316 and 316L, are mainly used. Therefore, the corrosion tests werecarried out mainly centered on the Cr content in a range of about 23 to30%; however, 16% chromium steel was also examined since examinations onlow-chromium steels were partially required.

The values close to the upper limit value of the amount of addition ofeach of alloy components, such as Ni, Mn, Mo and Cu, were selected inthe alloys of the present invention, that is, No. 5 alloy was selectedin the case of a low Cr content of 16%, Nos. 10 and 17 alloys wereselected in the case of Cr contents of 27% and 30% with valuable Mocontained therein, Nos. 16, 14 and 39 alloys were selected in the caseof varying Cr contents of 2%, 3% and 5.4% with no Mo contained therein,No. 22 alloy was selected in the case of a 10% Ni content, No. 28 alloywas selected in the case of a 8% Mn content, No. 29 alloy was selectedin the case of a 8% Mo content, and No. 30 alloy was selected in thecase of a 6% Cu content, and differences in corrosion were examined. Theresults of the examination are collectively shown in Tables 20 to 22.

TABLE 20 Various alloy chemical components used for corrosion resistancecomparisons Deposited chemical components (Cr, Ni: Content, Others:Amounts of addition) Charac- TP C Si Mo Cr Ni B Nb Cu Si × B teristics 5-C 1.5 2.5 4.5 16 7.5 1.0 4.0 4.6 2.5 Low chromium 10-C 0.7 3.6 4.6 277.5 2.4 0.5 4.5 8.6 with Mo 17-C 1.5 3.6 4.6 30 7.5 1.0 4.0 4.6 3.6 withMo 16-C 2.0 3.1 0 30 7.5 1.8 6.0 3.5 5.6 without Mo 14-C 3.0 4.1 0 307.5 1.8 6.0 3.5 7.4 without Mo No. 39 5.4 4.0 0 23 5.0 0 6.0 3.3 0without Mo 22-C 1.5 3.5 4.6 25 12.5 0.5 4.0 4.6 1.8 High Ni 28-C 1.5 3.54.6 24 7.5 0.5 6.0 4.6 1.8 High Mn Mn8 29-C 1.5 3.5 8.1 25 7.5 0.5 6.04.6 1.8 High Mo 30-C 1.5 3.5 4.6 25 7.5 0.5 6.0 6.0 1.8 High Cu

TABLE 21 Results of comparison tests for corrosion-resistant property ofvarious alloys 5% ferrous 10% sulfuric chloride Material Kind of steelsacid solution solution SS400 Mild steel 62.2 g  5.27 g SUS304 Stainless 9.6 g 0.105 g steel SUS310S Stainless  0.1 g  0.01 g steel Sulfuricacid Esten-1 steel 127.2 g   4.16 g resistant steel plate High chromiumWear-resistant 138.9 g   26.3 g cast iron cast iron GL Clad welding 48.3g  8.37 g rod UF Clad welding 17.4 g  4.93 g rod Stellite No. 1 Cladwelding 0.64 g  0.09 g bare rod Stellite No. 6 Clad welding 0.58 g  0.02g bare rod No. 5-C alloy Low Cr 0.17 g 0.116 g No. 10-C alloy with Mo0.56 g 0.037 g No. 17-C alloy with Mo 0.55 g 0.210 g No. 16-C alloywithout Mo 2.60 g 0.363 g No. 14-C alloy without Mo 2.80 g 1.404 g No.39 alloy without Mo 20.00 g  6.400 g No. 22-C alloy High Ni 0.03 g 0.155g No. 28-C alloy High Mn 0.06 g 1.486 g No. 29-C alloy High Mo 0.03 g0.034 g No. 30-C alloy High Cu 0.04 g 0.068 g

TABLE 22 Corrosion test against 10% hydrochloric acid aqueous solutionand 48% caustic soda aqueous solution 48% caustic 10% hydrochloric acidsoda aqueous Material solution solution SS400 28.00 g 0.0210 g SUS304 2.84 g 0.0008 g SUS310S  0.11 g 0.0006 g Sulfuric acid  2.42 g 0.0183 gresistant steel plate High chromium 101.39 g  0.0110 g cast iron GL32.58 g 0.0110 g UF 25.54 g 0.0040 g Stellite No. 1  0.11 g increasedweight Stellite No. 6  0.14 g increased weight No. 10-C alloy with Mo0.075 g 0.0023 g No. 17-C alloy with Mo 1.151 g 0.0130 g No. 16-C alloywithout Mo 1.080 g 0.0090 g No. 14-C alloy without Mo 0.277 g 0.0194 gNo. 39 alloy without Mo 0.435 g 0.0210 g

Since SUS310S was used as all the base materials for the corrosiontests, Cr was picked up from the base material so that the Cr contentwas increased. For example, in No. 10 alloy, the Cr content was 20% inthe bending ductility test in the graph; however, in the corrosion testpiece, the content was increased to Cr=27%. Here, since Cr and Ni wereof course picked up from the SUS310S base material, the contents of Crand Ni of the deposited metal were increased. With respect to corrosiontest numbers, following the numbered numeric value, C was put by takingthe first letter C of “Corrosion”. Therefore, all the alloys relating tothe corrosion tests were indicated as alloys-C.

(7) Concerning 10% Sulfuric Acid Corrosion (Relating to Alloys-C)

Comparisons of corrosive reductions caused by immersing them in a 10%sulfuric acid solution for 480 hours showed that No. 5, No. 22, No. 28,No. 29 and No. 30 alloys exerted a very good corrosion-resistantproperty in comparison with that of stellites No. 1 and No. 6. The wearcoefficient WR indicating the wear resistance was in a range of 8 to 10,which was the same level of the wear resistance as that of stelliteNo. 1. Here, No. 10 and No. 17 alloys exerted the same level of thecorrosion-resistant property as that of stellite, and the wearresistance thereof was the highest among the alloys of the presentinvention, with a wear coefficient WR of 3.3.

It was remarkable that these iron-based alloys exerted superior resultsin comparison with those of stellite alloys that are cobalt-basedalloys; therefore, in order to confirm the reliability of the results, a40% sulfuric acid solution corresponding to a concentration exerting asevere corrosive property was selected, and this solution was heated toa range from 50 to 70° C. so that by immersing test pieces into thissolution continuously four hours, the resulting amounts of corrosivereductions were compared with one another. Since it was difficult tocarry out corrosion tests again over 480 hours, accelerating tests for ashort period of time were carried out as simple confirming tests. Table23 shows the results of the tests.

TABLE 23 Results of 40% sulfuric acid solution-50 to 70° C. acceleratingcorrosion tests (Test time: 4 H) Various alloy Feature of alloyCorrosive reduction Stellite No. 1 C = 2.5%, 1.946 g cobalt-based alloyStellite No. 6 C = 1.2%, 1.667 g cobalt-based alloy No. 5-C Low Cr steel1.304 g No. 22-C 12.5% high Ni added 1.768 g steel No. 28-C 8% high Mnadded 1.687 g steel No. 29-C 8% high Mo added 1.679 g steel No. 30-C 6%high Cu added 2.331 g steel

In the accelerating tests also, the corrosion-resistant property againstsulfuric acid that was the same as, or higher than those of stellitesNo. 1 and No. 6 was exerted. In particular, No. 5 alloy was very good,and although No. 30 alloy was slightly inferior to stellite, there wasno big difference, and considered to be equivalent thereto.

Next, the effects of the carbon content exerted on corrosion resistanceagainst sulfuric acid were examined. Tables 24 and 25 show the resultsof the examination.

TABLE 24 Effects of carbon content exerted on corrosion resistanceagainst sulfuric acid Alloy No. C Si Cr Ni Mo Cu B 12-C 0.5 4.0 29 3.64.6 4.6 1.7 10-C 0.7 3.6 27 3.3 4.6 4.5 2.4 17-C 1.5 3.6 31 3.3 4.6 4.61.0 A 2.0 3.0 30 3.3 4.6 4.6 0 B 2.5 5.1 30 3.3 4.6 4.6 0 C 3.0 5.2 303.3 4.6 4.6 0

TABLE 25 Comparison of immersion tests for 480 hours Amount of 10%carbon 10% sulfuric hydrochloric TP No addition acid solution acidsolution 12-C 0.50 0.5925 0.0941 10-C 0.74 0.5608 0.0744 17-C 1.5 0.55151.1507 A 2.0 0.8425 0.4529 B 2.5 1.4840 0.1062 C 3.0 1.3470 0.1058

In a range of carbon content from 0.5%≦C≦3.0%, the correlation to thecorrosion resistance showed that the sulfuric acid corrosion was easilyinfluenced by the carbon content, and in the case of 2% or more, thecorrosion resistance against sulfuric acid tended to deteriorate. It isdetermined that boron gives no influences to sulfuric acid corrosion.Therefore, with respect to applications vulnerable to sulfuric acidcorrosion, the amount of carbon addition should be set to 2% or less.

With respect to sulfuric acid corrosion, conventionally, iron-basedwear-resistant metals are considered to be inapplicable; however, aniron-based alloy, which is a corrosion-resistant and wear-resistantmaterial, is superior to stellites No. 1 and No. 6 containing 50 to 65%of expensive cobalt, and has the same as, or higher than that of No. 1in wear resistance, has been invented. From the world-wide point ofview, consuming the stellite alloy containing a large amount of cobalthaving a rarity value for a simple wear-resistant purpose and forpurposes incapable of recovering resources is wasteful use of effectiveresources; therefore, the alloy of the present invention should be usedas an alternative metal for these from now on.

(8) Concerning Hydrochloric Acid Corrosion

With respect to hydrochloric acid corrosion, No. 29 alloy, No. 10 alloyand No. 30 alloy were superior to the stellite alloy, and in particular,in the corrosion-resistant tests against 10% hydrochloric acid solution,No. 10 alloy was superior to stellites No. 1 and No. 6, and it isimportant to use No. 10 alloy for the purpose of corrosion resistanceagainst hydrochloric acid.

The effects of the carbon content exerted on corrosion resistanceagainst hydrochloric acid were examined. With respect to the corrosionresistance against hydrochloric acid, only the numeric value of No. 17alloy exhibited a corrosive reduction about 10 times as high as those ofthe other alloys; however, no big differences were seen on the otheralloys, with no effects being caused on the deposited metal by thecarbon content. Certainly, stellite No. 1 had a tendency of beingstronger in the corrosion resistance against hydrochloric acid thanstellite No. 6 having a smaller carbon content, and different from thesulfuric acid corrosion, the corrosion resistance against hydrochloricacid is not affected by the amount of carbon addition.

In order to obtain the corrosion resistance as high as that of thestellite, an addition of expensive Mo is required. However, in recentyears, a unit price of Mo alloy has abnormally risen, with the resultthat the addition of a large amount of this causes serious effects tothe alloy cost, and might reduce the merit of using an inexpensiveiron-based alloy. Consequently, the present inventors try not to find acorrosion-resistant property as high as the stellite, but tosimultaneously invent an alloy that is superior in thecorrosion-resistant property in comparison with mutually the sameiron-based alloys. Those alloys are No. 16 and No. 14 alloys.

In comparison with high chromium cast iron produced by iron cast, No. 16alloy exhibited a corrosion-resistant property about 54 times higherwith respect to 10% sulfuric acid solution, about 72 times higher withrespect to 5% ferrous chloride solution, and about 94 times higher withrespect to 10% hydrochloric acid solution. Here, No. 14 alloy exhibitedvirtually the same tendency. In comparison with high carbon-highchromium cast-iron-type welding alloy GL, No. 16 alloy exhibited asuperior corrosion-resistant property about 19 times higher with respectto 10% sulfuric acid solution, and about 23 times higher with respect to5% ferrous chloride solution; thus, it has a superiorcorrosion-resistant property in comparison with conventionally usedhigh-chromium cast-iron-type alloys, and is proved to be sufficientlyapplicable to corrosion-resistant and wear-resistant purposes as theiron-based alloy.

EXAMPLES

The following description will discuss examples, and in comparison withcomparative examples, the effects of the present invention will beclarified. In recent years, along with the price hike of petroleum,import costs of coals have risen in association therewith, and ourcountry, which is lacking resources, is at present worried about fuelprice hikes. In particular, in coal thermal plants, iron works andcement factories where enormous amounts of coals are used, the amount ofuse of expensive good coals is reduced, while the use of mixed coalswith inexpensive coarse coals is increased. Among the coarse coals,coals having a great amount of sulfur content are present, and whenthese are stacked in stock yards outside, they get wet in rain, and havean increase in their moisture content, with the result that sulfurcomponents contained in the coal come to react with water to producediluted sulfuric acid.

In one example, a troughing conveyer is used in processes to introducecoals into a crusher, and since the bottom plate liner thereof isconventionally subjected to wear, a wear-resistant steel plate claddedwith a high-carbon-high chromium cast-iron-type alloy has been used forthis purpose. The chemical component thereof is a GL alloy that has beendescribed before. Here, since the start of using mixed coals having alarge amount of sulfur content, the service life thereof, which has beenlong since it has been subjected to simple wear, is shortened to onlyabout 2.5 months due to corrosion caused by diluted sulfuric acid. Whenthe developed alloy of the present invention was used as the bottomplate liner, neither corrosion nor wear has occurred therein, even aftera lapse of one year, and the bottom plate liner has been continuouslyused.

In order to prove deterioration of high Si-containing steel, beadphotographs were taken after the above-mentioned bending process. As atypical example, No. 55 alloy exhibited deterioration that was a defectof high Si-content, with the result that peeling were generated over theentire bead surface that had been pressed down by a press. However, inthe case of No. 10-C alloy corresponding to the alloy of the presentinvention, its toughness was proved in a bending process with 200R.

With respect to the amount of precipitation of chromium carbidedepending on differences in chromium content, No. 5 (Cr=16%)low-chromium content steel and No. 10-C (Cr=27%) high-chromium contentsteel were compared with each other in their micro textures. As shown inPhotograph 1 of FIG. 3 and FIG. 4, in the 10-C high-chromium contentalloy, plate-shaped crystals of coarse bulky chromium borate (Cr₂B) wereproduced, while no crystals were seen in No. 5 alloy. Therefore, alow-chromium steel may be used for applications subjected to heavyimpact wear, while a high-chromium steel may be used for applicationssubjected to only light impact wear.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a graph that shows effects of Si×B amount and Cr amountexerted on bending processability.

FIG. 2 includes photographs relating to alloy evaluations, andphotograph 1 is a microscopic photograph showing a needle-shaped textureof a conventional alloy, and photograph 2 is a photograph of a samplecross section indicating bent cracks of the conventional alloy.

FIG. 3 includes photographs, and photograph 1 is a microscopicphotograph showing a texture of alloy No. 10-C of the present invention,and photograph 2 is a photograph taken after a bent-crack test.

FIG. 4 is a microscopic photograph showing a texture of alloy No. 5 ofthe present invention.

1-3. (canceled)
 4. An alloy comprising: all percentages by weight, C:0.5 to 2.5%, Si: 2.5 to 4.5%, Mn: 10% or less, Cr: 15% to 31%, Cu: 7% orless, Mo: 10% or less, B: 0.5% to 3.5%, and 0≦Nb+V≦8%, wherein(Si×B)≦2014/Cr²+0.083Cr+1.05 when 15%≦Cr<27%, 1.25%≦(Si×B)≦6.0% when27%≦Cr≦31%, (Si×B)≧570/Cr²−0.066Cr+1.145 when 15% Cr<20%, and(Si×B)≧1.25 when 20%≦Cr≦31%.
 5. The alloy according to claim 4, furthercomprising: one kind or two or more kinds of Ni: 16% or less, Ti: 1.0%or less, Al: 3% or less, rare earth metals: 0.5% or less in total, andN: 0.2% or less.
 6. The alloy according to claim 4, wherein awear-resistant property and a corrosion-resistant property are the sameas, or superior to cobalt-based alloys, stellites No. 1 and No.
 6. 7.The alloy according to claim 4, in the form of clad welding metal orcast steel.
 8. The alloy according to claim 5, wherein a wear-resistantproperty and a corrosion-resistant property are the same as, or superiorto cobalt-based alloys, stellites No. 1 and No.
 6. 9. The alloyaccording to claim 5, in the form of clad welding metal or cast steel.